Abstract:
A brush configured to engage a rotating component to transfer an electrical signal and/or power is provided including a body formed from a core material. A coating material is disposed over a portion of the body configured to contact the rotating component. A contact area between the brush and the rotating component increases as the coating material wears.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Embodiments of the invention relate to aircraft propeller deicing systems, and more particularly, to brush block assemblies for use in propeller deicing systems. 
         [0002]    Propeller deicing systems are used to prevent ice build-up on an aircraft&#39;s propeller blades. The most common type of deicing system uses resistive heating elements, such as in the form of flexible strips for example, which are disposed along a section of the blade&#39;s leading edge closest to the hub assembly. The application of electrical current to the heaters weakens the bond between accumulated ice and the airfoil surface allowing the ice to be “thrown off” by the centrifugal forces generated by rotation of the propeller. 
         [0003]    An aircraft power source located on the non-rotating side of the propeller-engine interface provides electrical current to the brushes and through a rotating interface. The interface includes stationary, electrically conductive brushes which are in electrical contact with a conductive slip ring mounted to the rear of the rotating propeller&#39;s spinner assembly. Conventional slip rings are large in size, generally between two feet and three feet in diameter, and therefore require a significant amount of space within the propeller assembly. In addition, contact between the brushes and the conductive slip ring causes the ends of the brushes to wear unevenly. This uneven wear reduces the contact area between the brushes and the slip ring and therefore reduces the amount of electrical power that can be transmitted through the interface. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one embodiment of the invention, a brush configured to engage a rotating component to transfer an electrical signal and/or power to the rotating component is provided including a body formed from a core material. The body includes a portion configured to engage the rotating component. A coating material is disposed over the portion of the body configured to contact the rotating component. A contact area between the brush and the rotating component increases as the coating material wears due to operation of the rotating component. 
         [0005]    According to another embodiment of the invention, an assembly for transferring electrical power from a stationary component to a rotating component is provided including a shaft configured to rotate about a shaft axis. A slip ring assembly is mounted concentrically about the shaft, the slip ring assembly including a slip ring mounted to a plate face of a slip ring plate. A brush assembly including a brush has a first portion configured to contact the slip ring. A coating material is disposed over the first portion such that a contact area between the brush and the slip ring increases as the coating material wears due to rotation of the slip ring assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a schematic view of an embodiment of a propeller system of an aircraft; 
           [0008]      FIG. 2  is a partially cut away side view of a slip ring arrangement of a propeller system according to an embodiment of the invention; 
           [0009]      FIG. 3  is a cross-sectional view of another slip ring arrangement of a propeller system according to an embodiment of the invention; 
           [0010]      FIG. 4  is an end view of a brush block according to an embodiment of the invention; 
           [0011]      FIG. 5  is a cross-sectional view of a brush block engaged with a slip ring according to an embodiment of the invention and; 
           [0012]      FIG. 6  is a cross-sectional view of another brush block engaged with a slip ring according to an embodiment of the invention. 
       
    
    
       [0013]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Shown in  FIG. 1  is schematic view of an embodiment of a propeller system  10  for an aircraft. The propeller system  10  includes a propeller assembly having a plurality of propeller blades  12  arranged around a hub  14 . A pitch change actuator  11  is connected to an end of the hub  14 . The propeller blades  12  include one or more heating elements  30  for deicing of the propeller blades  12 . The propeller system  10  is operably connected to a reduction gearbox  16  via a propeller shaft  18 , which is in turn connected to an engine  20 . 
         [0015]    Referring now to  FIG. 2 , a spinner  22  encloses the hub  14  which mechanically secures each of the plurality of propeller blades  12  to the propeller shaft  18 . The rearward interior portion of the spinner  22 , facing the engine cowling  24 , includes a bulk head  26 . The bulk head  26  is both substantially flat and substantially annular in its geometry, and includes a center hole through which the propeller shaft  18  connects to the hub  14 . The exposed surface of the bulk head  26  includes a slip ring assembly  40 . Typically, a portion of the bulkhead  26  includes a slip ring plate  54  having a molded plastic composition configured to receive slip rings  42  (see  FIG. 6 ). The slip rings  42  are molded into or assembled to a plate face of the slip ring plate  54 . The slip ring plate  54  is concentric with the propeller shaft  18 , rearward of the hub  14 . 
         [0016]    A brush block  34  is located adjacent the bulkhead and is at least partially supported by and enclosed in a brush block housing  36 . The brush block  34  includes a number of brushes  46 , which interface with the slip rings  42  (see  FIG. 6 ). The brush block  34  receives electrical power from a power source, such as a generator (not shown) for example, and transfers the electrical power to the slip rings  42  via the brush block tips  46 . In the embodiment of  FIG. 2 , the brushes  46  extend substantially axially relative to the shaft axis  28  toward the slip rings  42 . The brushes  46  may be shimmed into a selected location relative to the slip rings  42 . A number of lead wires (not shown) extend from the slip rings  42  to the plurality of heating elements  30  mounted to the propeller blades  18 . 
         [0017]    In another embodiment, illustrated in  FIG. 3 , the slip ring plate  54  is a generally cylindrical tube, similar to a sleeve, concentric with and secured to the propeller shaft  18 , rearward of the gearbox  16 . The at least one slip ring  42  of the slip ring assembly  40  is molded into or assembled about the circumference of the plate face  56  such that the brushes  46  form an interface with the slip rings  42  as the shaft  18  rotates about a shaft axis  28 . Although particular slip ring assemblies  40  configured for use in a propeller assembly  10  are illustrated and described in the disclosed non-limiting embodiments, slip rings assemblies having other configurations or used in other applications outside of aircrafts are within the scope of the invention. 
         [0018]    Referring now to  FIGS. 4 , an example of a brush block  34  is illustrated in more detail. The brush block  34  includes an injection molded housing  36  have a plurality of brush pockets or chambers  60 . In one embodiment, the brush pockets  60  are generally arranged in a column or row. The geometry of the housing  36  is determined by the particular engine and/or aircraft model type so as to provide secure mounting of the brush block  34 . The plurality of electrically conductive brushes  46  are slidably received within the plurality of brush pockets  60  formed in the housing  36 . The brushes  46  are shown having a generally rectangular cross-section, but other cross-sectional shapes are within the scope of the invention. Biasing means (not shown) are provided for urging an exposed end  62  of each brush  46  into contact with a surface of an adjacent slip ring  42 . Thus, the brushes  46  and the slip rings  42  form a plurality of sliding contacts. Electrical power is conducted from the brushes  46 , through the plurality of sliding contacts to the rotating slip ring  40 . 
         [0019]    With reference to the configuration illustrated in  FIGS. 2 and 6 , the slip rings  42  are substantially flat, circular plates. The exposed ends  62  of the brushes  46  are similarly flat to maximize contact with the flat surface of the slip rings  42 . In system of other configurations, as shown in the embodiment illustrated in  FIG. 5 , the brush block  34  is mounted generally perpendicular to the propeller shaft  18  such that the exposed ends  62  of the brushes  46  are configured to engage the outer diameter of the slip ring  42 . To increase the contact area between the brushes  46  and the slip rings  42 , the exposed end  62  of each brush  46  includes a radial cut, generally complementary to the curvature of the slip ring  42 . Though certain brush designs are illustrated and described herein, other configurations are within the scope of the invention. 
         [0020]    Referring now to both  FIGS. 5 and 6 , each brush  46  comprises a core material  70  and a coating material  72 . The core material  70  substantially forms the body of the brush  46  and may be any conductive material, such as carbon, graphite, or some combination thereof for example. The coating material  72  is generally a thin layer of a soft, conductive material uniformly applied over at least a portion of the surface  64  of the brush  46  configured to engage the slip ring  42 . In one embodiment, the coating material  72  is configured to wear more quickly than the core material  70  to improve the contact formed between the brush  46  and the slip ring  42 . Exemplary coating materials  72  include, but are not limited to, soft nickel, copper, carbon, and a silver containing conductive compound or paint for example. The coating material  72  and the core material  70  may be integrally formed during manufacturing, such as through a single step injection molding process for example. Alternatively, the body of the brush  46  may be formed from the core material  70  first, and the coating material  72  may be applied in a separate process afterwards, such as with a spray for example. 
         [0021]    Initial engagement of the slip ring  42  and brushes  46  will result in wear of a portion of the coating material  72  of each brush  46 . As the coating material  72  wears, the conformity between the slip ring  42  and the exposed end  62  of the brush  46  generally improves. By selecting a soft coating material, the time required to achieve a desired contact area between the slip ring  42  and each of the brushes  46  is reduced. As a result of this increased surface contact at each of the plurality of sliding contacts, additional power can be delivered to the heating elements  30 . 
         [0022]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.