Patent Description:
Icing of aerodynamic surfaces is a well-known problem in the art of aeronautics. Icing can be partly mitigated by on-ground application of chemical compounds to prevent formation or adhesion of ice particles on the aerodynamic surfaces. However, with particular reference to open rotor aircraft propulsion systems, on- ground treatments have not proven generally effective for the duration of flight. Accordingly, various in-flight de-icing systems and methods have been used. For example, ice can be removed by microwave power impinging upon adsorbing structures on rotor blades to separate ice from the blade, as disclosed for example by <CIT> and <CIT>. Equally, electrical heating elements can be mounted on rotor blades to separate ice from the blades, as disclosed for example by <CIT>.

Known in-flight de-icing methods for propulsion rotors require transfer of power from the main airframe to the propulsion rotors. There are several difficulties with the various known methods for transferring power from the main airframe to the rotors of a contra-rotating open rotor aircraft propulsion system. Mechanical power transfer requires rotating contact between components that wear, bind, slip, and/or add undesirable weight and/or friction to the propulsion rotor assembly. Optical beam power transfer is susceptible to interference from opaque materials, and typically requires a fixed line-of-sight not easily achieved in a contra-rotating propulsion rotor system. Fluid power transfer along a contra- rotating propulsion rotor system requires provision of complex seals and fluid passages that are susceptible to wear and leakage. Radiative power transfer is difficult to focus, therefore prone to leakage that increases thermal management requirements of the propulsion system. Electrical power transfer, using slip ring assemblies, is a very common method that has proven failure modes associated with arcing caused by hydraulic fluid mixing with carbon dust formed by the slip ring brushes. Additionally, due primarily to brush wear, slip ring assemblies are high maintenance items requiring servicing on the order of hundreds of hours of operation. Within contra-rotating propulsion systems, the maintenance requirements associated with slip rings become both more frequent (because the contra-rotating elements rotate at higher relative speed, causing greater rates of brush wear) and more problematic (because at least one slip ring is "buried" within the contra-rotating shaft assembly). Moreover, in a typical contra-rotating propulsion system, one of the propulsion rotors is arranged distally from the main airframe. In such a typical contra-rotating propulsion system, electrical power can be provided from the main airframe to the distal propulsion rotor only through a sequence of two slip rings. Sequential arrangement of slip rings reduces the efficiency of power transfer, and also significantly worsens the chance of a failure in the overall electrical power transfer system.

The document <CIT> discloses an electrical de-icing equipment for aircraft including heaters energized from a generator which rotates, together with its field windings, with a propeller, and an armature being adapted to rotate in the opposite direction and so provide a high speed of relative rotation.

The document <CIT> discloses a configuration of DC motor/generator based on a Halbach array of permanent magnets.

The document <CIT> discloses a rotor arrangement for an electric machine having a rotor body and permanent magnets embedded in the rotor body.

With the foregoing problems and concerns in mind, it is the general object of the present invention to provide a system of power transfer, within a contra-rotating open rotor aircraft propulsion system, which overcomes the above-mentioned drawbacks.

An electrical power generation apparatus includes first and second shafts. A winding is mounted to the first shaft. An electrical load mounted to the first shaft is electrically connected to receive electrical current from the winding. A field array is mounted to the second shaft adjacent to the winding. The first shaft and the second shaft are operatively connected for relative rotation of the first shaft and the second shaft. Relative rotation of the first and second shafts induces an electrical current in the winding to power the electrical load.

An electrical power generation apparatus is embedded in a contra-rotating propulsion system that includes overlapping first and second shafts operatively connected for counter-rotation about a common axis. The electrical power generation apparatus includes a winding mounted to one of the shafts and a field array mounted to the other of the shafts adjacent to the winding. Relative rotation of the winding and the field array induces electrical current in the winding.

A contra-rotating open rotor aircraft propulsion system includes first and second overlapping shafts operatively connected for counter-rotation about a common axis. Each shaft includes a rotor blade set. The propulsion system further includes a de-icing apparatus, which at least includes a first de-icing element mounted to one of rotor blade sets, a winding mounted on the shaft corresponding to the rotor blade set having the de-icing element, and a field array mounted on the other shaft adjacent to the winding. Relative rotation of the winding and the field array induces an electrical current in the winding to power the de-icing element, thereby de-icing the rotor blade set having the de-icing element. The present invention thereby provides electrical power to rotating parts of a contra-rotating mechanical system without requiring an electrical connection or a mechanical connection between the rotating parts for purposes of power transfer.

Referring to <FIG>, a jet aircraft <NUM> can be propelled by a contra-rotating open rotor propulsion system <NUM>, which is controlled by an avionics package (not shown). The contra-rotating open rotor propulsion system <NUM> includes a jet engine <NUM> or similar prime mover, which drives a forward open rotor blade set <NUM> and an aft open rotor blade set <NUM> disposed aft of the jet engine in a "pusher configuration". Alternatively, the forward and aft rotor blade sets can be disposed forward of the jet engine in a "tractor configuration". Throughout the following detailed description of the drawings, the forward rotor blade set should be regarded as exemplary of a rotor blade set disposed proximate to the jet engine, and the aft rotor blade set should be regarded as exemplary of a rotor blade set disposed distal from the jet engine. The forward and aft rotor blade sets contra- rotate about a common axis <NUM> defined by the jet engine. For example, the forward shaft can be driven by the jet engine to rotate in a clockwise (CW) direction and the aft shaft can be driven by the jet engine to rotate in a counterclockwise (CCW) direction.

Referring to <FIG>, forward and aft de-icing apparatus <NUM>, <NUM> are mounted near leading edges of the forward rotor blade set <NUM> and of the aft rotor blade set <NUM>, respectively, for melting ice that forms on the rotor blade sets during flight. For example, the forward and aft de-icing apparatus may be electrical resistance heating elements. The forward blade set is mounted oh a forward shaft <NUM> extending aft from the jet engine. The aft open rotor blade set is mounted on an aft shaft <NUM> extending aft from the forward rotor blade set. The aft shaft is radially nested within the forward shaft to be driven by a common gear set (not shown) disposed within the jet engine. The aft shaft is rotatably supported within the forward shaft by bearings <NUM>.

The forward and aft de-icing apparatus are electrically connected to receive conditioned electrical current from forward and aft power control and conditioning units <NUM>, <NUM>, respectively. The forward power control and conditioning unit is connected to receive electrical current from a forward permanent magnet (PM) generator <NUM>. The aft power control and conditioning unit <NUM> is connected to receive electrical current from an aft permanent magnet (PM) generator <NUM>. Each power control and conditioning unit is configured to selectively interrupt, modulate, clip, or otherwise modify the electrical current passing from the associated generator to the associated de-icing apparatus.

The forward and aft PM generators are mounted next to each other on the forward and aft shafts <NUM>, <NUM>, within an axial overlap region <NUM> defined by the nested axial ends of the forward and aft shafts adjacent to the bearings <NUM>. Preferably, the forward and aft PM generators are mounted within an oil-mist- cooled volume <NUM> contained by the forward and aft shafts, so that oil spray jets (not shown) can cool the PM generators. The disposition of the PM generators at an axial distance from the bearings mitigates heat transfer between the bearings and the PM generators. The radial gap arrangement of the PM generators provides for ease of assembly, but imposes tighter dimensional tolerances on the shaft assembly than would be required if the PM generators were disposed adjacent to the bearings.

The forward permanent magnet generator includes a forward winding <NUM> mounted on the forward shaft and a forward permanent magnet array <NUM> mounted on the aft shaft, radially opposing the forward winding. The aft permanent magnet generator includes an aft winding <NUM> and an aft permanent magnet array <NUM> mounted at radially opposing locations on the aft and the forward shafts, respectively. Thus, as shown in <FIG>, each PM generator has a winding radially opposing a complementary cylindrical array of permanent magnets. The radial-gap configuration of the forward and aft PM generators provides for ease of assembly. Each permanent magnet array acts as a field array providing a magnetic field that rotates with reference to the corresponding winding for inducing an electrical current in the corresponding winding.

Typically, each permanent magnet array includes magnetically soft material, or "back iron", for flux guidance and shielding of the array. The permanent magnets may be manufactured of any sufficiently coercive permanent magnet material such as Alnico, Neodymium Iron Boron, or Samarium Cobalt.

The winding of the forward PM generator is electrically connected to provide electrical current to the forward de-icing apparatus through the forward power control and conditioning unit <NUM>. The winding of the aft PM generator is electrically connected to provide electrical current to the aft de-icing apparatus through the aft power control and conditioning unit <NUM>. The forward power control and conditioning unit is electrically connected to receive control signals from the avionics package (not shown) via a forward rotary signal transfer transformer <NUM>, and also is electrically connected to send control signals to the aft power control and conditioning unit via an aft rotary signal transfer transformer <NUM>. Thus both of the forward and aft de-icing apparatus can be controlled in tandem by the avionics package.

Referring to <FIG>, the forward and aft de-icing apparatus <NUM>, <NUM> can alternatively be configured to receive electrical current from forward and aft Halbach-array generators <NUM>, <NUM>. The forward Halbach-array generator includes an inner winding <NUM> and a forward flat circular Halbach array pair <NUM>. The inner winding of the forward Halbach-array generator is mounted to protrude radially outward from the forward shaft <NUM>. The forward flat circular Halbach array pair is mounted to protrude radially inward from the aft shaft <NUM>, forward and aft of the inner winding. The aft Halbach-array generator includes an outer winding <NUM> and an aft flat circular Halbach array pair <NUM>. The outer winding of the aft Halbach-array generator is mounted to protrude radially inward from the aft shaft24. The aft flat circular Halbach array pair <NUM> is mounted to protrude radially outward from the forward shaft, forward and aft of the outer winding.

The windings of the forward and aft Halbach-array generators are electrically connected to provide electrical current to the forward and aft power control and conditioning units <NUM> and <NUM>, respectively. The forward and aft Halbach-array generators are mounted within an oil-free volume <NUM> provided between the forward and aft shafts <NUM>, <NUM> and are air-cooled. The axial gap configuration of the Halbach-array generators and the disposition of the Halbach-array generators axially proximate to the bearings <NUM> mitigate dimensional tolerance requirements for the shaft assembly as a whole.

Referring to <FIG>, a typical linear Halbach array <NUM> includes a plurality of permanent magnets <NUM> arranged to form repeating patterns of pole faces along a working surface <NUM> and along a shielding surface <NUM> opposed to the working surface. In <FIG>, each "N" indicates a "north" pole face <NUM> having magnetic flux directed substantially perpendicularly outward from the N pole face; each arrow indicates a side face <NUM> having magnetic flux directed substantially along the side face in the direction of the arrow; and each "S" indicates a "south" pole face <NUM> having magnetic flux directed substantially perpendicularly into the south pole face. As arranged in the typical linear Halbach array, the N pole faces, side faces, and S pole faces reinforce a magnetic field <NUM> adjacent to the working surface and cancel or severely constrain the magnetic field adjacent to the shielding surface. The reinforced magnetic field repeats in a cyclic fashion along the working surface of the typical linear Halbach array.

Referring back to <FIG>, the forward flat circular Halbach array pair <NUM> includes a plurality of wedge-shaped permanent magnet sections <NUM> arranged in two axially-opposing flat circular Halbach arrays <NUM>, <NUM>, which are disposed forward and aft, respectively, of the forward winding <NUM>. The aft flat circular Halbach array pair similarly includes two axially-opposing flat circular Halbach arrays <NUM>, <NUM>. Each of the flat circular Halbach arrays <NUM>, <NUM> has a working surface <NUM> that faces the opposite Halbach array, and has a shielding surface <NUM> that faces away from the opposite Halbach array.

Referring to <FIG>, each of the flat circular Halbach arrays includes N pole permanent magnet sections <NUM>, transitional permanent magnet sections <NUM>, and S pole permanent magnet sections <NUM>. Each of the flat circular Halbach arrays has eighteen (<NUM>) poles - nine (<NUM>) N pole pieces and nine (<NUM>) S pole pieces - circumferentially distributed at twenty degree (<NUM>°) intervals, with five transition pieces between each N pole piece and the following S pole piece, for a total of two hundred and sixteen (<NUM>) permanent magnet sections in each Halbach array pair <NUM>, <NUM>.

Each Halbach array <NUM>, <NUM> is about <NUM> millimeters (mm) thick axially and has a <NUM> centimeter (cm) outer diameter and a <NUM> inner diameter for a radial width of about <NUM>. Each Halbach array generator <NUM>, <NUM> has an axial thickness of about <NUM> with <NUM> axial air gaps between each winding and the adjacent working surfaces of the associated Halbach array pair. Each pole piece <NUM>, <NUM> covers approximately <NUM>° along the Halbach array pair circumference, while the transition pieces <NUM> occupy <NUM>° between each adjacent pair of N and S pole pieces. The permanent magnet sections <NUM> can be built with alnico, neodymium iron boron, or samarium cobalt to have permanent magnet density of about <NUM>/cm3 and magnet coercive force of about <NUM> kA/m.

As shown in <FIG> and <FIG>, the forward flat circular Halbach array pair <NUM> is arranged with a circumferential offset so that N pole pieces <NUM> in the forward and aft Halbach arrays <NUM> and <NUM> are opposed to S pole pieces <NUM> in the aft and forward Halbach arrays <NUM> and <NUM>, respectively, thereby forming a circumferential pattern of alternating magnetic dipoles between the working surfaces <NUM> of the forward flat circular Halbach array pair. The aft flat circular Halbach array pair <NUM> is similarly arranged. The circumferential pattern of alternating magnetic dipoles provides a substantially axially-directed magnetic field <NUM> that varies circumferentially between the working surfaces <NUM>, while containing substantially all magnetic flux between the axially outward shielding surfaces <NUM>. Each Halbach array pair <NUM>, <NUM> thereby provides electromagnetic self-shielding for the associated Halbach-array generator <NUM>, <NUM>. Because the Halbach array pairs provide self-shielding, the Halbach-array generators can be built substantially without "back iron" typically used for magnetic field containment.

Referring to <FIG>, the inner winding <NUM> of the forward Halbach array generator <NUM> includes a plurality of conductive coils <NUM>, <NUM> arranged in a circumferential array matching the flat circular patterns of N and S pole pieces in the associated Halbach array pair. The outer winding <NUM> of the aft Halbach array generator <NUM> includes a similar circumferential array of coils. Each winding has twenty seven (<NUM>) <NUM>° intervals. The coils of the windings are built with <NUM> turns per coil and a <NUM>/<NUM> coil-to-pole coverage ratio (each coil occupying approximately <NUM>° of the winding circumference). The winding configuration shown in <FIG> can also be utilized in the permanent magnet generators <NUM>, <NUM>.

Referring to <FIG>, between the inward working surfaces <NUM> of each Halbach array pair, the magnitude of the reinforced axial magnetic field <NUM> is substantially sinusoidal with respect to a circumferential angle Θ around the generator central axis <NUM>. Thus the magnetic flux φ that is coupled by a single conductive coil <NUM> or <NUM> within one of the windings, can be calculated according to <MAT> as shown in <FIG> for a coil <NUM> within the inner winding <NUM> of the forward Halbach array generator <NUM>.

For a single conductive coil <NUM> or <NUM> that covers two thirds of the corresponding pole piece <NUM> or <NUM>, taking the minimum field intensity at zero radians mechanical, and assuming phase A is aligned with zero radians mechanical, the back electromotive force for phase A can be calculated according to <MAT> in volts RMS, where ωm is the mechanical rotational velocity in radians per second, Ncoil is the number of coils per phase, Ns is the number of turns per coil, r is the average radius in meters, / is the height of the magnet section in meters, m<NUM> is the permeability of free space and the permanent magnet in henries per meter, l_m is the thickness of the magnet in meters, w_mag is the width of the magnet section in meters, l_ap is the average length of the flux air path including the permanent magnet path in meters, Hc is the coercive force of the permanent magnet in amps per meter, and qr is the angle between the rotor quadrature axis and phase A of the stator. The back EMF for phase A is at a maximum when qr is zero radians.

The inductance per phase can be calculated in henries according to <MAT>.

In operation, referring particularly to <FIG> and <FIG>, the contra-rotating open rotor aircraft propulsion system <NUM> is driven at a machine mechanical speed of twenty cycles per second (<NUM> or <NUM> RPM) so that the forward and aft shafts <NUM>, <NUM> rotate at a relative speed of <NUM> RPM causing each of the twenty seven (<NUM>) coils <NUM>, <NUM> to cross three hundred and sixty (<NUM>) dipoles per second. At operational speed, presuming approximately zero (<NUM>) ohms armature resistance, approximately zero Tesla (<NUM> T) leakage flux, <NUM> A/mm<NUM> current density in the windings, and <NUM> ohms load resistance per phase, and modeling the Halbach array permanent magnet sections <NUM> as infinitely thin surface conductors, the eighteen (<NUM>) poles of each Halbach array pair induce <NUM> kilowatts of three phase alternating current in each winding at two hundred eight (<NUM>) volts RMS and three hundred sixty cycles per second (<NUM>), for a power factor of <NUM>. The volume of active material, including the windings and the Halbach array pairs <NUM>, <NUM>, is <NUM> liters, and the mass of the active material is <NUM> kilograms, for a total electrical power / weight ratio of <NUM> kW / <NUM>.

One advantage of the present invention is that, by using the contra-rotation of the shafts to generate electrical power in the same rotational frames as the open rotor blades, the electrical power generation apparatus permits provision of electrical power to the open rotors without requiring mechanical, optical, fluid, radiative, or electrical connections, contact, or communication between the contra-rotating portions of the propulsion system for purposes of power transfer. More specifically, according to one embodiment of the present invention, contra- rotating permanent magnet generator windings arranged on a forward shaft and an aft shaft within the contra-rotating propulsion system are respectively electrically connected, via power control and conditioning units, to de-icing heater elements disposed at leading edges of the contra-rotating forward rotor blades and aft rotor blades.

Another advantage of the present invention is that the electrical power generating apparatus disclosed herein permits provision of electrical power to a distal propulsion rotor in a contra-rotating propulsion system, without using slip rings. As will be appreciated in view of the present disclosure, eliminating the use of slip rings generally reduces maintenance requirements. Specifically within a contra-rotating propulsion system, eliminating the use of slip rings provides substantial advantages for efficiency, reliability, and ease of maintenance. In particular, because the generators of the present invention do not require brush maintenance, the generators can be conveniently embedded within the propulsion system without limiting the propulsion system design for the sake of frequent maintenance access.

Additionally, the present invention provides a capability of embedded electromechanical power conversion within a contra-rotating open rotor aircraft propulsion system, without induction of eddy currents in adjacent rotating frames. More specifically, according to another embodiment of the present invention, paired Halbach arrays of permanent magnets are embedded into contra-rotating shafts of an aircraft propulsion system to provide axial flux path electromagnetic machines (Halbach-array generators) that deliver electrical current to rotor blade de-icing apparatus. Each Halbach-array generator includes a rotating winding that is mounted to the same rotating structure as are the rotor blades requiring de-icing power, and also includes a self-shielded magnetic field source that does not rotate with the rotating coil structure. By providing a self-shielding magnetic field source, the Halbach arrays substantially eliminate any need for magnetic flux guidance or containment using "back iron" or ferromagnetic steel shield rings.

Although the Halbach arrays typically require a slightly greater volume and weight of permanent magnet than would be needed for more conventional permanent magnet motor arrangements, the elimination of "back iron" and associated weight reduction more than compensates for the added weight of the Halbach arrays themselves. Additionally, the Halbach arrangement reduces or eliminates torque ripple and electrical harmonics. The magnetic coupling in an axial flux path of the dual magnet groups to the coils eliminates wear and is efficient.

Another advantage of the present invention is that the mutually aligned Halbach arrays form magnetic dipoles so that, between axially facing surfaces of the Halbach arrays, the axial magnetic flux intensity varies as the sinusoid of the circumferential angle around the central axis of the permanent magnet section. Outside the axially outward surfaces of the Halbach arrays, the magnetic flux is essentially zero magnitude to provide a self-shielding characteristic. Current induced in the rotating winding by relative angular motion of the self-shielded Halbach array pair powers the rotor blade de-icing apparatus.

Another advantage of the present invention is that contra-rotation of the field arrays and the generator windings provides for doubled relative rotational speed within the mechanical limits of the arrays and windings, thereby producing greater electrical currents than could be achieved with known generator arrangements of similar size and weight.

Claim 1:
A contra-rotating aircraft propulsion system (<NUM>) with an electrical power generation apparatus comprising:
a first shaft (<NUM>);
a first rotor blade set (<NUM>) mounted to said first shaft (<NUM>) and configured to propel the aircraft;
a first winding (<NUM>) mounted to said first shaft (<NUM>); a first electrical load (<NUM>), being a first de-icing element of the first rotor blade set (<NUM>), mounted to said first shaft (<NUM>) and electrically connected to receive electrical current from said winding (<NUM>);
a second shaft (<NUM>);
a second rotor blade set (<NUM>) mounted to said second shaft (<NUM>) and configured to propel the aircraft; and
a first permanent magnet field array (<NUM>) mounted adjacent to said first winding (<NUM>) on said second shaft (<NUM>),
wherein said first shaft (<NUM>) and said second shaft (<NUM>) are operatively connected so that the second shaft (<NUM>) contra-rotates relative to said first shaft (<NUM>) about a common axis, so that rotation of said first permanent magnet field array (<NUM>) relative to said first winding (<NUM>) induces an electrical current in said first winding (<NUM>) to power said first electrical load (<NUM>), and the first rotor blade set (<NUM>) and the second rotor blade set (<NUM>) contra-rotate;
the apparatus further comprising:
a second winding (<NUM>) mounted to said second shaft (<NUM>) and extending toward said first shaft (<NUM>);
a second permanent magnet field array (<NUM>) mounted to said first shaft (<NUM>) and adjacent to said second winding (<NUM>);
a second electrical load (<NUM>), being a second de-icing element of the second rotor blade set (<NUM>), mounted to said second shaft (<NUM>) and electrically connected to receive electrical current from said second winding (<NUM>);
a first power control unit (<NUM>) electrically connected between said first winding (<NUM>) and said first de-icing element to modify said electrical current;
and
a second power control unit (<NUM>) electrically connected between said second winding (<NUM>) and said second de-icing element to modify said electrical current.