Rotor containment brake

A generator and process for operating a generator in which, upon a bearing failure, a braking force is applied to the rotor shaft responsive to the bearing failure. Preferably, the rotor shaft at the anti-drive end is hollow and the brake is provided in the hollow of the rotor shaft. The rotor can include a plate member extending radially inwardly from the rotor shaft inside of the hollow at the anti-drive end towards the longitudinal axis, with the brake applying the braking force to the plate member. In a preferred aspect, the brake includes a cylindrical support operably connected to the housing and extending into the hollow in the anti-drive end of the rotor shaft, a carrier plate connected to the support and extending radially from the support towards the rotor shaft, a screw thread provided on the support, and a threaded plate mounted on the screw thread, the threaded plate extending radially from the support towards the rotor shaft and being spaced from the carrier plate. Rotation of the threaded plate about the support causes the threaded plate to move towards the carrier plate, pressing the plate member of the rotor between the carrier plate and the threaded plate, thereby applying braking force thereto.

BACKGROUND OF THE INVENTION
 The present invention relates to a generator including a rotor containment
 brake for applying a braking force to a rotor and to a process for
 operating the generator, including applying a braking force to the rotor
 upon bearing failure.
 Generators for generating electricity in aircraft applications are
 generally operated at high speeds, e.g., in the range of 12,000 to 30,000
 rpm. At such high operating speeds, a failure of the rotor bearings can
 cause catastrophic damage, e.g., by having parts thrown through the
 housing, thereby damaging other aircraft parts. It is known in the art to
 disconnect rotor shafts from the driving source, e.g., a gear box shaft,
 either through use of a shear section or by a non-shear type disconnect,
 the latter of which is disclosed in U.S. Pat. No. 3,620,045.
 However, the disconnect systems known in the art do not operate
 instantaneously. That is, there is a delay between the occurrence of
 bearing failure and the disconnect. During the delay, there is a
 possibility the rotor parts will not be sufficiently contained within the
 generator housing. Accordingly, there is still a need to provide a
 mechanism for restricting prolonged rotor rotation immediately after
 bearing failure.
 SUMMARY OF THE INVENTION
 The present invention relates to a generator and process for operating a
 generator in which, upon a bearing failure, a braking force is applied to
 the rotor shaft responsive to the bearing failure. Preferably, the rotor
 shaft at the anti-drive end is hollow and the brake is provided in the
 hollow of the rotor shaft. The rotor can include a plate member extending
 radially inwardly from the rotor shaft inside of the hollow at the
 anti-drive end towards the longitudinal axis, with the brake applying the
 braking force to the plate member. In a preferred aspect, the brake
 includes a cylindrical support splined to the housing and extending into
 the hollow in the anti-drive end of the rotor shaft, a carrier plate
 fixedly connected to the support and extending radially from the support
 towards the rotor shaft, a screw thread provided on the support, and a
 threaded plate mounted on the screw thread, the threaded plate extending
 radially from the support towards the rotor shaft and being spaced from
 the carrier plate. Rotation of the threaded plate about the support causes
 the threaded plate to move towards the carrier plate, pressing the plate
 member of the rotor between the carrier plate and the threaded plate,
 thereby applying braking force thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 shows the cross-sectional view of a generator 10. The generator 10
 is, for example, a generator for supplying electricity to an aircraft. The
 generator shown in FIG. 1 is, e.g., of the type used as a back-up
 generator for a Boeing 777. The basic structure of such a generator is
 known in the art, with the generator 10 shown in FIG. 1 having been
 modified to provide a rotor containment brake according to the present
 invention.
 The generator 10 includes a main housing 12 in which a rotor, generally
 designated by the reference numeral 14, is supported. The rotor 14
 includes a rotor shaft 16 supported in the housing 12 by ball bearing 18
 and roller bearing 20. The rotor shaft includes an input shaft 22 which is
 connected to a driving source, e.g., a gear box shaft from a reducing gear
 box from the engine. The rotor 14 includes a rotor core 24, a rotor sleeve
 26 and main field windings 28. The anti-drive end of the rotor 14, i.e.,
 the end opposite the input shaft 22, includes a pump drive section 30
 connected to a pump gear set 32 for operating a supply pump 34 having pump
 impeller 36 connected to scavenge inlet 38. A vacuum brake valve 40 is
 also provided.
 The rotor 14 is provided with a rectifier bridge 42, while the housing 12
 is also provided with a main armature 44, an exciter stator 46 and a
 permanent magnet generator (PMG) armature 48. Such a generator can
 generate electricity for the electrical system of an aircraft as is known
 in the art.
 The generator 10 has been modified to provide a rotor containment brake,
 generally designated by the reference numeral 50. The rotor containment
 brake is provided in a hollow 52 and the anti-drive end of the rotor shaft
 16, e.g., adjacent the PMG armature.
 As can be seen generally in FIG. 1 and in more detail in FIG. 2, the rotor
 containment brake 50 includes a cylindrical support 54 which can be
 operably connected to a modified top pump plate 56. In the preferred
 embodiment shown in FIG. 1, the support 54 is mounted within an extension
 57 which is attached to top pump plate 56 by, e.g., bolt 59. The support
 54 is held within extension 57 during normal operation of the generator 10
 by, e.g., a split ring retainer 61 mounted in slots in support 54. During
 braking, as will be apparent from the description hereinafter, the support
 54 can move axially within the hollow 52.
 A carrier plate 58 extends radially outwardly from the support 54 towards
 the rotor shaft 16. The carrier plate 58 can be integral with the support
 or mounted in any manner, but in this embodiment is prevented from
 rotating. Support 54 is provided with a screw thread 60. A threaded plate
 62 is mounted on the support 54 and held in place during normal operation
 of the generator by, e.g., a shearing soft pin 64. The threaded plate
 could also be held on the support by a detent ring or the other means
 which will hold threaded plate 62 in position during normal operation but
 will be sheared upon bearing failure, as will be explained hereinafter.
 During normal operation of the generator, i.e., while rotor shaft 16
 rotates while being supported by bearings 18 and 20, a gap or clearance 66
 is maintained between the rotor shaft 16 and the radially outer end of
 threaded plate 62. However, upon bearing failure, the clearance 66 closes,
 i.e., the inside diameter of rotor shaft 16 within hollow 52 hits against
 threaded plate 62. It is preferred that the portion of rotor 16 adjacent
 threaded plate 62 has a high friction surface 17 and/or that the radial
 outermost end of threaded plate 62 has a high friction surface 63. The
 high friction surface can be a grooved surface or can be a high friction
 material. When the rotating rotor shaft 16 hits the threaded plate 62 upon
 bearing failure, the rotating rotor shaft 16 creates torque to turn
 threaded plate 62, thereby shearing soft pin 64 and screwing threaded
 plate 62 towards carrier plate 58.
 The rotor shaft 16 is provided with a plate member 68. The plate member 68
 is fixed to the inside diameter of the rotor shaft 16 in hollow 52, e.g.,
 by being integral to a removable splined nut part screwed into the rear of
 the rotor. The plate member 68 can also be attached to rotor shaft 16 by a
 spring loaded or shear plug retained, guided diameter instead of a spline
 support. As threaded plate 62 is screwed along screw thread 60 towards
 carrier plate 58, the plate member 68 is grabbed between carrier plate 58
 and threaded plate 62, thereby applying a braking force to rotor shaft 16.
 It is preferred that the mating surfaces of threaded plate 62 and plate
 member 68 also be provided with high friction surfaces 63 and 17,
 respectively, e.g., a grooved surface or a high friction material. When
 threaded plate 62 screws into contact with plate member 68, support 54 is
 pulled out of the position in which it was retained (during normal
 operation by split ring 61) towards plate member 68, pinching plate member
 68 between threaded plate 62 and carrier plate 58.
 In an alternative embodiment, the carrier plate 58 can be threaded in the
 opposite direction as threaded plate 62, so that, upon bearing failure,
 both plates 58, 62 are screwed towards plate member 68.
 The rotor containment brake 50 herein described should have adequate
 strength to sustain rotor braking until the disconnect, e.g., shear
 section, disconnects the rotor shaft 16 from the gear box shaft. While the
 braking may cause damage, this condition is considered acceptable for
 accomplishing rotor containment since the real damage has already occurred
 prior to brake actuation.
 While the invention has been described in terms of its preferred
 embodiments, it should be understood that numerous modifications may be
 made thereto without departing from the spirit and scope of the invention
 as defined in the appended claims. It is intended that all such
 modifications fall within the scope of the appended claims.