Patent Application
20050091849
(1) Field of the Invention
The present invention relates to a system for operating a variable vane in a gas turbine engine having improved wear characteristics and more particularly to a thrust washer constructed of electro-graphitic carbon for reducing wear used in said system.
(2) Description of the Related Art
In gas turbine engines, the variable vanes of the high pressure compressor are rotated via a trunnion assembly. With reference to
In the past, the thrust washer 23 has been typically constructed of a wear resistant and low friction material such as graphite filled polyimide materials capable of continuous operation up to 650° F. The thrust washers 23 constructed of such polyimide materials are not capable of withstanding the high temperatures and loads of advanced high performance compressors. Potentially, this is a problem because it is necessary to avoid metal to metal contact between the vane platform 21 of the variable vane 17 and the outer split case 22. Such metal to metal contact could serve to degrade the vane platform 21 and the outer split case 22 and alter the physical geometry of each and induce higher friction in the variable vane kinematic system. Geometric alterations are undesirable because they can result in an undesirable angular displacement of the variable vane 17. Specifically, if a variable vane 17 is displaced with respect to adjacent vanes by more than 6°, a less than optimal operating scenario may be induced. It is therefore important that the vane platform 21 and the outer split case 22 operate in such a manner as to maintain their shapes, and, thus, maintain a constant variable vane angle.
What is therefore needed is a thrust washer which does not suffer material breakdown at high temperatures and which serves to maintain the fit and orientation of the vane platform 21 and the outer split case 22.
Accordingly, it is an object of the present invention to provide a system for operating a variable vane in a gas turbine engine having improved wear characteristics and more particularly to a thrust washer constructed of electro-graphitic carbon for reducing wear used in said system.
In accordance with the present invention, a method for improving the wear characteristics of a system for operating a variable vane comprises the steps of providing a trunnion connected to the variable vane via a vane platform and means for causing rotation of the trunnion, and positioning a thrust washer formed from a carbon material about a lower portion of the trunnion and in a space between the vane platform and an outer split case so that during operation of the system the space between the vane platform and the outer split case is maintained substantially constant and unwanted deflection of the vane is avoided.
In further accordance with the present invention, a system for operating a variable vane in a gas turbine engine comprises a vane, a trunion attached to the vane for rotating the vane, and means for avoiding unwanted deflection of the vane at operating temperatures, the deflection avoiding means comprises a self lubricating thrust washer surrounding a lower portion of the trunnion.
It is a teaching of the present invention to provide a variable vane operating system having a thrust washer 23 composed of a carbon based substance, preferably electro-graphitic carbon. It has been suprisingly found that the use of such a thrust washer in a variable vane operating system is advantageous in a high temperature environment because the washer does not suffer significant breakdown even at temperatures approximating 1050° F. In addition, a thrust washer formed from such a material both self lubricates as well as maintains the appropriate distance between the vane platform 21 and the outer split case 22. As used herein, “self lubricate” refers to the ability of the thrust washer of the present invention to degrade through a process of depositing the electro-graphitic carbon from which it is constructed onto the engine components with which it is in contact. As a result of this deposition, the volume originally occupied by the thrust washer remains filled with electro-graphitic carbon of the same volume throughout operation, thus maintaining the original geometry and orientation of the vane platform and outer split case. The thrust washer of the present invention may operate for extended periods of time at high temperatures while maintaining its geometry so as to avoid unwanted deflection of the variable vane.
With reference to
Tests conducted at 850° F. confirm that a thrust washer 23 formed from an electro-graphitic carbon material in accordance with the present invention exhibits a 3.5X wear resistance over the washers known in the art over a sixty-five hour period and continued to run up to 207 hours with the same amount of wear as a polyimide designed washer experienced at sixty-five hours.
During installation of the thrust washers of the present invention, some geometric adjustments to the inner and outer diameters may have to be made to accommodate thermal expansion rate. This is because carbon materials such as electro-graphitic carbon have a lower thermal expansion rate than polyimide materials. In addition, chamfers and/or blending of edges may be required to minimize pinch points at the fillet radius of the vane trunnion. Without these adjustments, pre-mature spallations/cracking could occur from the edges.
It is apparent that there has been provided in accordance with the present invention an improved operating system for a variable vane which fully satisfies the objects, means, and advantages set forth previously herein. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
