Patent Application
20060137355
The invention relates generally to an aircraft generator and, more particularly, to an improved emergency electrical power generating apparatus for use with an aircraft gas turbine engine having a fan assembly.
In modern turbofan powered aircraft, an emergency power source is required for control of flight surfaces in the event of total loss of the availability of the primary power sources, i.e. engine driven hydraulic pumps and/or engine driven electrical generators. In small airplanes this power is provided by the energy stored in aircraft batteries. In larger airplanes, a single ram air turbine, or RAT with an integral generator or hydraulic pump is provided for deployment in emergency situations only. The emergency power source is the aircraft's own air speed (kinetic energy) and altitude (potential energy). However, a RAT must be positioned away from the aircraft surfaces and is usually mounted under the wing or below the nose of the aircraft. It can present significant challenges in aircraft design to find a suitable location for the RAT and to design a deployment system to position on the RAT for deploying same into the air stream. In order to avoid those challenges and other disadvantages of RAT systems, emergency electrical generators coupled with a low pressure spool of engines, have been developed to use the kinetic energy and potential energy provided by the fan assembly of the engine, during a windmill action thereof. Nevertheless, the conventional fan-driven emergency generator systems are not satisfactory for various reasons.
Accordingly, there is a need to provide an improved fan-driven emergency electrical power generating apparatus and a method for use of same with aircraft turbofan engines.
It is therefore an object of this invention to provide an emergency electrical power generating apparatus and a method for use with an aircraft gas turbine engine having a fan assembly.
In one aspect, the present invention provides an emergency electrical power generating apparatus for use with an aircraft gas turbine engine having a fan assembly, which comprises an electrical generator and a clutch assembly for connecting the electrical generator with the fan assembly to transfer torque from the fan assembly during a windmill action of the fan assembly, and for disconnecting the generator from the fan assembly during engine operation.
In another aspect, the present invention provides an emergency electrical power generating apparatus for use with an aircraft gas turbine engine having a fan assembly, which comprises an electrical generator stator mounted to a housing of a bearing, and an electrical generator rotor mounted to one of a fan shaft and a low pressure spool shaft supported directly on said bearing.
In another aspect, the present invention provides a method for generating emergency electrical power using a windmill action of an aircraft gas turbine engine, which comprises disconnecting torque transmission from the engine to an emergency electrical power generator during engine operation; and connecting torque transmission from the engine to the emergency electrical power generator during the windmill action.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
An engine core casing 36 is provided to support the low pressure and high pressure spool assemblies 12 and 18, thereby defining an annular main fluid path of the engine therethrough and an annular bypass duct 38 between the nacelle 10 and the engine core casing 36. A tailcone 40 is provided at the aft end of the engine core casing 36 for directing exhaust gases discharged from the aft end of the engine core casing 36. The tailcone 40 defines a tailcone compartment 42 therein which accommodates an emergency electrical power generating apparatus 50 according to one embodiment of the present invention.
The emergency electrical power generating apparatus 50 includes an electrical generator 52 coupled with a clutch assembly 54 at an output end thereof and the clutch assembly 54 at an input end thereof is coupled with the low pressure spool shaft 17. Thus, the electrical generator 52 is driven to rotate by torque transmitted from the low pressure spool shaft 17 when the clutch assembly 54 is engaged. The electrical generator 52 is not in operation when the clutch assembly 54 is disengaged.
Selective engagement of the clutch assembly 54 is arranged to meet requirements such that during normal engine operating conditions the clutch assembly 54 is disengaged to disconnect the generator from the low pressure spool shaft 17, and during a windmill action of the fan assembly 11 when the engine has failed to function, the clutch assembly 54 is engaged to connect the electric generator with the low pressure spool shaft 17. The low pressure spool shaft 17 is coupled with the fan shaft (not shown) and is rotated together with the fan assembly 11, thereby transferring torque from the fan assembly 11 to the electrical generator 52 during the windmill action. Therefore, the electrical generator 52 is only operated to provide emergency electrical power to the aircraft in emergency situations in which the engine has failed to function.
The speed increasing gearset 56 can be any type of gearbox configuration. As a preferred example, the gearset 56 as illustrated in
Referring to
The speed increasing ratio of the speed increasing gearset 56 is generally designed to increase the operative speed of the electrical generator 52 from a relatively low rotational speed of the low pressure spool shaft 17 during a windmill action of the fan assembly 11. Under normal engine operating conditions, however, the fan assembly 11 and the low pressure spool 12 are rotated by the low pressure turbine 15 at a rotational speed much higher than the rotational speed of the low pressure spool shaft 17 during a windmill action of the fan assembly 11. If the emergency electrical power generating apparatus 50′ did not include clutch assembly 54 and the speed increasing gearset 56 was directly coupled to the low pressure spool shaft 17, speed increasing gearset 56 would drive the electrical generator 52 at a rotational speed much higher than the required operative speed of the electrical generator 52. It is therefore desirable to avoid unnecessary operation of the electrical generator 52 under such overspeed conditions.
Various types of clutch assemblies can be used, for example, clutch assembly 54 can be a centrifugal clutch, which is disengaged to disconnect the electrical generator 52 from the low pressure spool shaft 17 when the input side of the clutch assembly 54 coupled with the low pressure spool shaft 17 is rotated at a higher rotational speed range under normal engine operating conditions, and which is engaged to connect the electrical generator 52 to the low pressure spool shaft 17 when the input end of the clutch assembly 54 coupled with the low pressure spool shaft 17 is rotated at a low speed range during a windmill action of the fan assembly 11. The centrifugal clutch is automatically controlled by the change in input speed. However, the component indicated by numeral 54 in either
The clutch assembly 54 can be various other types of clutch which can be controlled manually, or automatically such as being electrically or hydraulically controlled by a controller 72, as shown in
The emergency generator does not absolutely need to be in the engine core location. An alternative configuration could have the unit mounted inside the nacelle on the fan case area (same general location as the accessory gearbox). In this arrangement the towershaft would extend through a strut and into the nacelle area to the clutch generator unit.
In the embodiment of
The electrical generator rotor 84 includes at least one, but preferably a plurality of permanent magnets 94 attached to an annular support member 96. The annular support member 96 is mounted at an inner periphery thereof on the fan shaft 90, and has an axially extending flange 98 for the attachment of the permanent magnets 94 thereto such that the permanent magnets 94 are positioned around and slightly radially spaced apart from the electrical generator stator 82. Thus, the electrical generator stator 82 and rotor 94 in combination form an electrical generator incorporated with the Number 1 bearing assembly.
It should be noted that the configuration of the electrical generator stator 82 and rotor 94 including the annular support member 96, are examples to illustrate the configuration of an electrical generator incorporated with a bearing assembly. The stator and rotor of the electrical generator incorporated with a bearing assembly according to this invention may have alternative structural arrangements. For example, stators may include permanent magnets and rotors may include electric windings. Furthermore, the annular support member 84 can be replaced by other configurations which have substantially similar functions for supporting the rotor in the operative position and transmitting torque to the rotor.
It also should be noted that according to the present invention, the emergency electrical power generating apparatus 80 can be incorporated with any bearing assemblies which directly support one of the fan shaft and low pressure spool shaft of a gas turbine engine having a fan assembly.
It should be noted that similar to the clutch assembly 54 described in the other embodiments and illustrated in
The addition of clutch assemblies 54 and 54′ to the emergency electrical power generating apparatuses 50, 50′, 80 and 80′, further advantageously provides an option to allow testing of the emergency electrical power generating apparatus during engine start up, in which the fan shaft and the low pressure spool are driven by the low pressure turbine at a low rotational speed range similar to that provided by a windmill action in an emergency situation. Once the engine is accelerated above this rotational speed range, the clutch assemblies will disconnect the emergency electrical power generating apparatus from the operative engine and thereby discontinue the testing procedure.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, emergency electrical generator may be replaced by an emergency hydraulic pump, or the present invention can be applicable to an aircraft engine having propellers. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the scope of the appended claims.
