Patent Application
20070175709
This invention relates to carbon-carbon composite brake discs, and more particularly, to brake disc drive inserts for use in carbon-carbon composite brake discs. The present invention provides an improved friction surface in annular drive inserts that are received rotatably within generally annular openings within a brake disc.
Large aircraft typically include brake assemblies which employ a plurality of brakes discs alternatingly splined to the wheel and non-rotating brake frame of the aircraft. Carbon-carbon composite brake discs, because they have improved braking and heat sink characteristics as well as weight advantages, have become the brake discs of choice for this application. However, carbon-carbon composite brake discs generally have less strength than comparable steel discs. It is important therefore to provide specially constructed drive means to reinforce the peripheral slots in the discs and to relieve the severe stressing that otherwise would rapidly deteriorate the periphery of the discs. Among the patents that describe inserts are U.S. Pat. Nos. 3,800,392, 3,934,686, 3,972,395, 4,007,814, 4,083,434, 4,465,165, 4,469,204, 4,511,021, 4,557,356, 4,784,246, 5,273,140, 5,560,452, and U.S. Pat. No 5,634,535.
U.S. Pat. No. 5,273,140 (Fred W. Berwanger) describes a brake disc annular drive insert. The drive insert described by Berwanger comprises a generally cylindrical member with radially extending flanges at opposite axial ends thereof. The Berwanger drive insert includes a generally cylindrical body having an opening at one side thereof which extends diametrically into the body and terminates at a point between the center of revolution of the body and an outer surface of the body. The opening in the body extends to an inner surface of the body to provide a generally rectangular opening for receiving a spline of a torque tube. The Berwanger drive insert is typically made of steel. The flanges of the Berwanger drive insert may comprise either generally annular flanges shaped complementary with the generally cylindrical body and or may be truncated at a side opposite the opening in the body. In his
The present invention provides an improvement on the brake disc annular drive insert described in U.S. Pat. No. 5,273,140. The present invention protects the stator drive slots from wear. Of course, the carbon-carbon composite insert employed in this invention will be subject to wear. However, the C-C insert is easily replaceable. Also, this invention provides a low friction interface for torque tube splines. Thus the present invention also increases braking torque.
The Berwanger design provides wear resistance to the carbon-carbon composite disc drive slot by flanges on the insert which prevent relative axial motion between these two parts. Relative axial motion occurs between the insert and the torque tube spline. Inasmuch as the coefficient of friction between the insert and the spline is greater than that between a bare drive slot and the spline, the normal force between the brake discs is reduced, resulting in lower brake torque.
The present invention provides a low friction material bed within the steel insert with flanges described by Berwanger. In the practice of the present invention, the steel insert with flanges may be manufactured with a cut-out area designed to receive the low friction material bed. The low friction material bed of the present invention may be made of carbon-carbon composite material, and is preferably cylindrical in shape. It is retained within a complementary (e.g., cylindrical) cavity in the steel insert by radially inward extending flanges at opposite ends thereof. The geometry of the insert and its steel sheath naturally retains the carbon insert in place, in much the same way that the steel insert assembly is retained in place in the carbon brake disc itself. It is simply rotated into position, and once installed into a brake, it is impossible to rotate loose.
Thus this invention provides brake disc drive inserts for use in carbon-carbon composite brake discs. A rotatable brake disc annular drive insert in accordance with the present invention includes a cylindrical steel body having one side of the body truncated to provide an insert opening which extends axially through the body. The insert opening extends into the body along a diameter of the body and the insert opening terminates at a radially extending surface located between the revolutional center of the body and an outer surface of the body. End flanges extend radially outwardly from the outer surface of the body to provide for axial positioning of the drive insert relative to a brake disc. Unlike in previously known drive inserts, in accordance with this invention the drive insert opening has a lining comprising carbon-carbon composite material. The resulting low friction carbon-carbon composite material bed that is positioned between the steel insert component and the torque tube spline location pursuant to this invention provides significantly lower friction and enables significantly greater disc clamping and brake torque.
The rotatable brake disc drive insert lining of carbon-carbon composite material in accordance with this invention may be made with nonwoven fiber matrices or with random fiber matrices. These fiber matrices may be needled to reduce the possibility of chipping in the final product.
In accordance with this invention, the insert opening in the rotatable brake disc drive insert body may be cylindrical in shape. The insert bodies themselves are typically about 0.75 inches in diameter and from 0.75 to 1.5 inches in length. The opening extending into the insert lining is generally rectangular in shape to provide a seat for a spline member of a torque tube. Each of the end flanges extending from the cylindrical steel body may have a truncated portion disposed opposite from the one side of the body. However, any convenient dimensions and configurations may be employed with the invention described herein.
In a preferred embodiment of the present invention, the brake disc containing rotatable brake disc drive inserts of the invention is a stator. Accordingly, the present invention also contemplates a brake disc stator that includes a plurality of the rotatable brake disc annular drive inserts described herein.
An aircraft carbon-carbon composite brake disc is generally annular in shape and includes an outer diameter circumference and a central generally annular opening. Located about the periphery of the opening is a plurality of slot openings or recesses receiving therein brake disc annular drive inserts. These recesses are generally annularly shaped slots extending radially outwardly from the opening of the disc. These annular drive inserts couple a torque tube with the disc, the torque tube being non-rotatably coupled with an axle of an aircraft. The torque tube includes radially extending short splines which extend within the openings of respective annular drive inserts. Each annular drive insert comprises a generally cylindrical body that rotatably engages the surface of a recess on the periphery of the opening in the annular carbon-carbon composite brake disc. The body of the insert is truncated at one side and provides an opening which extends diametrically into the cylindrical body. The opening extends past the center of revolution of the body and terminates in a surface (which may or may not be flat) located between the center of revolution and the outer surface of the cylindrical body. At opposite axial ends of the cylindrical body are radially extending flanges that engage opposite sides of the disc to retain the drive insert axially within the annularly shaped slot (that is, within the recess in the carbon-carbon composite brake disc).
In accordance with the present invention, the insert opening has a lining made of carbon-carbon composite material. The shape of the cavity in the steel insert which receives the lining will generally be the same as that of the outside diameter of the carbon-carbon composite insert. When the lining cavity in the steel insert is cylindrical, then a cylindrical outer shape for the carbon-carbon composite insert fits rotatably into the steel insert and is self-retained without adhesive. Employing similar surface shapes in this manner facilitates distribution of load between the parts and minimizes bearing stress. In an alternative embodiment where the two surfaces are not cylindrical, adhesive may be required. This is generally not desirable, however, because replacement of the carbon-carbon composite insert due to wear will be more difficult if adhesive is used.
Although the above description refers to the annular drive inserts in combination with a stator brake disc and a torque tube, the drive insert of the present invention can also be located rotatably in an annular recess at the outer circumferential edge surface of a rotor disc in order to couple the rotor disc with an aircraft wheel. The wheel would include either an integral axially extending drive boss or an attached drive key to provide a drive member coupled with the rotatable drive insert in the same manner that the torque tube spline is coupled with the drive insert rotatably positioned in the recess of the stator brake disc.
Further details on brake disc annular drive inserts can be found in U.S. Pat. No. 5,273,140 (Berwanger), the entire disclosure of which patent is hereby expressly incorporated by reference.
Specifics of the present invention are described with reference to the drawings which accompany this application.
With reference to
As illustrated in
The present invention is not limited as to dimensions of the rotatable brake disc annular drive insert lining or of the steel body of the brake disc into which it is inserted. Typical insert bodies in accordance with this invention are 0.75 inches in diameter and from 0.75 to 1.5 inches in length. However, other sizes may likewise be appropriate in individual circumstances. In accordance with this invention, the carbon-carbon composite drive insert lining rests inside the steel insert body. Accordingly, its dimensions are selected to be proportional to the steel insert body. For instance, for a steel body 1.5 inches long with a wall having a thickness of 0.10 inches on both ends and an outer diameter of 0.75 inches, the carbon-carbon insert lining would be approximately 1.3 inches long and 0.55 inches in diameter. In accordance with this invention, the drive insert lining will normally have a slot that is slightly larger than the torque tube spline along which it slides. That is, the width of the slot in the carbon component will be slightly greater than the width of the torque tube spline.
In the present invention, wear resistance is provided just as it is with the Berwanger design. However, the low friction carbon-carbon composite material bed that is positioned between the steel insert component and the torque tube spline location provides significantly lower friction and enables significantly greater disc clamping and brake torque.
