Abstract:
A system and method can be utilized to determine an out of balance condition of a rotor having a plurality of blades. The system monitors a clearance between the blades and an associated housing. By looking at a center of that clearance information, a determination can be made of the magnitude of imbalance of the rotor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a system which utilizes blade clearance information to identify the magnitude and location of a rotor imbalance. 
         [0002]    Gas turbine engines include a plurality of sections mounted in series. Typically, a fan may deliver air into a compressor section. The air is compressed and delivered downstream into a combustion chamber where it is mixed with fuel and combusted. Products of that combustion pass downstream over turbine rotors. 
         [0003]    The fan, the compressor, and the turbines all include rotors with attached blades. 
         [0004]    It is known to monitor the tip clearance of at least some of the blades of these rotors. Such monitoring may be utilized to determine potential problems with the rotors or the blades. It is known to utilize microwave signals, and monitor a reflected signal to identify a tip clearance. 
         [0005]    One other feature that is often monitored with regard to such rotors is rotor imbalance. If the rotors are out of balance, severe vibration can occur, which is undesirable. To date, engine rotor balance technology has required special test instrumentation or ground support equipment. Installing this instrumentation is time consuming, and requires the engine to be out of service for a period of time. The ground support equipment is limited, and there is often a wait to obtain this equipment. 
       SUMMARY OF THE INVENTION 
       [0006]    In the disclosed embodiment of this invention, the results from a blade clearance sensor are utilized to identify the magnitude of imbalance of a rotor. The same information can be utilized to determine the location of the imbalance. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a gas turbine engine. 
           [0009]      FIG. 2  is a system for identifying an imbalance with regard to a rotor in the  FIG. 1  system. 
           [0010]      FIG. 3  is a sample result for performing the method of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0011]      FIG. 1  illustrates selected portions of an example gas turbine engine  10 , such as a turbofan gas turbine engine used for propulsion. In this example, the turbine engine  10  is circumferentially disposed about an engine centerline  12 . The turbine engine  10  includes a fan  14 , a compressor section  16 , a combustion section  18 , and a turbine section  20 . The combustion section  18  and the turbine section  20  include corresponding blades  22  and vanes  24 . As is known, air compressed in the compressor section  16  is mixed with fuel and burned in the combustion section  18  to produce hot gasses that are expanded in the turbine section  20 .  FIG. 1  is a somewhat schematic presentation for illustrative purposes only and is not a limitation on the disclosed examples. Additionally, there are various types of gas turbine engines, many of which could benefit from the examples disclosed herein and are not limited to the designs shown. 
         [0012]      FIG. 2  shows a system  50  for identifying an imbalance for a rotor  52  having a plurality of blades  54  spaced from a housing  53 . While this invention may relate to any number of rotors having blades, in particular, it is well suited for the rotors such as are found in a gas turbine engine. A probe  56  may be utilized to determine a clearance between the outer tip of the blades  54  and the inner surface  53  of the housing. Such sensors are in use today, and are known in the art. 
         [0013]    The probe  56  may communicate with a coupler  58 , and receive microwave signals from a source  60 . A detector  62  may detect a reflected signal, and submit that detected signal to processing electronics  64 . The processing electronic  64  may also be provided with a signal  65  indicative of the completion of a rotation cycle. Such systems are known, and have been utilized in the past for determining blade clearance. 
         [0014]    The present invention is directed to utilizing the blade clearance information to determine an imbalance of the rotor  52 . As shown in  FIG. 3 , a series of clearances for multiple rotation of a rotor having 58 blades might well look like as shown at B c . As can be appreciated, this clearance information is offset relative to a center C 1  of the rotor. The offset of the B C  information relative to the center C 1 , is indicative of the rotor being out of balance. 
         [0015]    Known processing techniques can be utilized on the B C  information. As an example, fast forward transforms can be utilized, or any other way of calculating a center of the information B C  can be utilized. The center of that information is shown at C A . This is the apparent center, due to the imbalance. The distance d between C 1  and C A  is the magnitude of the displacement of the center of mass, and is indicative of the magnitude of the imbalance. An angle θ can be defined between any point, and a location of C A . As shown in  FIG. 3 , the location of the number one blade to the location of the apparent center C A  is utilized to determine θ. By determining θ, the location of the center of the imbalance can be determined. A worker of ordinary skill in this art with knowledge of the apparent center and θ, would know how to provide a counterweight to correct the imbalance. 
         [0016]    Since the present invention utilizes sensor technology that is already incorporated into gas turbine engines for other purposes, no new instrumentation is necessary to achieve the invention. Moreover, since this existing sensor is utilized, the present invention can provide imbalance information in real time, and without taking the engine out of service. As an example, if on one flight an incident occurred that could have affected the balance of the rotor, the electronics would have been able to identify the change in the imbalance, and could provide a warning to a pilot. An example display  67  may be utilized to provide such a warning to the pilot that the rotor imbalance has exceeded a magnitude that had been preset as a limit. 
         [0017]    Alternatively, the system can also be utilized to provide routine maintenance information, and the location to which a counterweight can be attached to correct the imbalance. 
         [0018]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.