Patent Publication Number: US-7707902-B2

Title: Apparatus for measuring bearing thrust load

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 11/352,635, filed Feb. 13, 2006 now U.S. Pat. No. 7,430,926, which is hereby incorporated by reference and is assigned to assignee of the present invention. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and, more specifically to measuring a bearing thrust load on gas turbine engine bearing assemblies. 
   At least some known gas turbine engines include rotating compressors and turbines. The rotating compressors and turbines are supported within a case by bearing assemblies. During operation, thrust loads may be induced to the bearing assemblies that damage and/or reduce an operational life of such bearing assemblies. Accordingly, bearing thrust forces are sometimes monitored to determine if such forces are high enough to damage and/or reduce the operational life of such bearing assemblies. 
   Bearing thrust loads are sometimes measured using strain gages secured to races of the bearing assemblies. For example, the strain gages are sometimes calibrated in a laboratory and thereafter installed in the bearing races. At least some known bearing races may need to be reworked so that the gages can be securely engaged to the races. However, reworking bearing surfaces and calibrating each strain gage may be time consuming and difficult. 
   At least some known strain gage configurations for measuring bearing thrust loads include leadout wires that are routed through static structures of the gas turbine engine to a power source and measurement circuit. If the wires are incorrectly connected to the measurement circuit, the thrust readings can be reversed, i.e., the thrust load may be indicated as being in a direction opposite the direction of the actual thrust load. Also, with the above described strain gage configuration, the readout wires secured to the internal engine surfaces may work loose over time, possibly resulting in a loss of signal. In addition, the strain gage readout may be dependent upon temperature correction. To compensate for temperature affects on the gages, it may be necessary to mount temperature sensors in the region of the strain gages, which may add complexity to the installation and measurement. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a bearing rotor thrust sensor assembly is provided for being secured to a bearing housing having a plurality of fingers extending between a pair of opposite portions of the housing. The assembly includes a first anchor member including a first cleat and configured to couple to a first housing portion of the pair of opposite housing portions, a second anchor member including a second cleat and configured to couple to a second of the pair of opposite housing portions, and a head sensor bracket positioned at least partially between the first and second anchor members. The head sensor bracket includes a load cell including a bridge circuit for producing a signal representative of forces on said cell. 
   In another aspect, a rotor bearing includes a housing and a bearing rotor thrust sensor assembly coupled to the housing without using an adhesive. The bearing rotor thrust sensor assembly includes a load cell including a bridge circuit for producing a signal representative of forces on the cell. 
   In another aspect, a method is provided for securing a bearing rotor thrust sensor assembly to a bearing housing having a plurality of fingers extending between a pair of opposite portions of the housing. The method includes coupling a head sensor bracket to a first and a second anchor member at least partially therebetween, positioning a first cleat of the first anchor member adjacent a first opening within a first housing portion of the pair of opposite housing portions, positioning a second cleat of the second anchor member adjacent a second opening within a second housing portion of the pair of opposite housing portions, and spreading the first and second anchor members apart such that the first cleat is received within the first opening, the second cleat is received within the second opening, and the first and second cleats each impart a force to the respective first and second housing portions to facilitate fixedly secure the assembly to the bearing housing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is perspective view of an exemplary embodiment of a bearing rotor thrust sensor assembly. 
       FIG. 2  is a side view of an exemplary engine bearing in which the assembly shown in  FIG. 1  may be utilized. 
       FIG. 3  is a perspective view of the bearing rotor thrust assembly shown in  FIG. 1  secured to the bearing shown in  FIG. 2 . 
       FIG. 4  is a circuit schematic diagram of an exemplary embodiment of a load cell for use with the sensor assembly shown in  FIG. 1 . 
       FIG. 5  is a schematic block diagram of an exemplary embodiment of sensing circuit for use with the sensor assembly shown in  FIGS. 1 and 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a perspective view of an exemplary embodiment of a bearing rotor thrust sensor assembly  10 . Assembly  10  mounts to a bearing housing (not shown in  FIG. 1 ) and includes a head sensor bracket  12  positioned at least partially between a pair of anchor members  14  and  16 . More specifically, head sensor bracket  12  is coupled to anchor members  14  and  16  at least partially therebetween. In the exemplary embodiment, head sensor bracket  12  is coupled to anchor member  14  via a turnbuckle  18 , and bracket  12  is received within an opening  20  of anchor member  16  and coupled thereto using any suitable structure and/or means, such as, but not limited to welding. Turnbuckle  18  changes a distance between anchor members  14  and  16  to facilitate securing assembly  10  to the bearing housing, as will be described in more detail below. Assembly  10  may mount to the bearing housing in any suitable configuration, arrangement, fashion, and/or by any suitable structure and/or means. For example, in the exemplary embodiment, each anchor member  14  and  16  includes a respective cleat  22  and  24  extending outwardly therefrom for reception within a corresponding opening (not shown in  FIG. 1 ) within the bearing housing, as will be described in more detail below. Although each anchor member  14  and  16  is illustrated as including only one cleat  22  and  24 , respectively, each anchor member  14  and  16  may include any number of cleats  22  and  24 , respectively, for reception within any number of openings in the bearing housing. In the exemplary embodiment, head sensor bracket  12  is hollow so that it facilitates reducing a reduced mass as compared to a solid bracket and facilitates reducing vibration response and loading during operation. 
   Head sensor bracket  12  includes a load cell  26 , which is sometimes referred to herein as a sensing element. In some embodiments, load cell  26  is coupled to bracket  12  using any suitable structure and/or means, such as, but not limited to, welding and/or using threaded fasteners. In other embodiments, load cell  26  is integrally formed with bracket  12 . Load cell  26  is fabricated from a metallic substrate with a screen printed thick film pattern of multiple layers. Although load cell  26  may be fabricated from any suitable metallic substrate, in some embodiments load cell  26  includes steel, such as, but not limited to 4340 alloy steel. In some embodiments, load cell  26  is coated with a corrosion protective coating and includes a strain gage bridge, a temperature sensor, and fault protection, as described below. Generally, load cell  26  has a double cantilever head configuration with strain sensing material between both cantilever supports. 
   In the exemplary embodiment, anchor member  16  includes an opening  28  for containing a portion of a pair of wire cables  30  and  32  that each include a twisted pair of wires  34 ,  36 ,  38 , and  40 , respectively. Wires  34  and  36  are soldered to load cell  26  and provide an excitation voltage to load cell  26 . Wires  38  and  40  are also soldered to load cell  26  and carry the cell output to a sensing circuit (not shown in  FIG. 1 ). In some embodiments, one or more solder joints between load cell  26  and wires  34 ,  36 ,  38 , and  40  is covered with epoxy in order to impart a greater resistance to handling and vibration damage. 
   A pushrod  42  extends from a body  44  of anchor member  16  and into contact with load cell  26 . As such, pushrod  42  is positioned to impart a force to on load cell  26  to, for example, provide the desired pre-load on load cell  26  and/or deflect load cell  26  during axial movement of the bearing housing, which will be described in more detail below. In some embodiments, a position of pushrod  42  is adjustable relative to a body  44  of anchor member  16  to facilitate adjusting the pre-load on load cell  26 . Anchor member  16  also includes one or more springs  46  that facilitate relative movement between head sensor bracket  12  and pushrod  42 . Springs  46  may also facilitate providing that the amount of axial motion imparted by pushrod  42  to load cell  26  can be maintained to within the movement capability of load cell  26 . Although springs  46  may each include any suitable shape, in the exemplary embodiment springs  46  are shaped as illustrated herein. 
     FIG. 2  is an isometric side view, partially in cross section and with parts cut away, of an exemplary engine bearing housing  50  in which assembly  10  (shown in  FIG. 1 ) may be utilized. Bearing housing  50  includes a sump housing  52  and a bearing support bracket  54  extending from sump housing  52  to support a bearing assembly  56 . A plurality of finger supports  58 , sometimes referred to herein as fingers, extend between portions  60  and  62  of bracket  54 . Only one such finger  58  is shown in  FIG. 2 . Bearing assembly  56  includes an inner race  64  and an outer race  66 , and a ball bearing  68  is positioned between races  64  and  66 . A rotating component  70  is secured to inner race  64  and as component  70  and inner race  64  rotate, loads (e.g., an aft load force direction is shown in  FIG. 2 ) are exerted on bearing assembly  56 . In some embodiments, a plurality of guides (not shown) are located around the circumference of bearing housing  50  to provide guidance for wire cables  30  and  32 . 
     FIG. 3  is a perspective view of bearing rotor thrust assembly  10  secured to bearing housing  50 . Assembly  10  may mount to the bearing housing in any suitable configuration, arrangement, fashion, and/or by any suitable structure and/or means. In the exemplary embodiment assembly  10  is secured to housing  50  between adjacent fingers  58  and such that assembly  10  is generally parallel to housing fingers  58 . Specifically, cleat  22  is positioned adjacent an opening  72  within bearing housing portion  60 , and cleat  24  is positioned adjacent an opening  74  within bearing housing portion  62 . Using turnbuckle  18 , anchor members  14  and  16  are then spread apart such that cleat  22  is received within opening  72 , cleat  24  is received within opening  74 , and cleats  22  and  24  each impart a force to bearing housing portions  60  and  62 , respectively, to facilitate fixedly securing assembly  10  to bearing housing  50 . 
   As bearing housing  50  is put into either tensile or compressive loading, an axial dimension of housing  50  is changed, for example from about 0 to +/− about several mils. Pushrod  42  moves with this axial dimensional change of bearing housing  50 , and as pushrod  42  moves, the loading (or deflection imparted) on load cell  26  also changes. By sensing the deflection changes on load cell  26 , the loading on bearing housing  50  can be determined. Springs  46  facilitate relative movement between pushrod  42  and head sensor bracket  12 , and therefore load cell  26 . Springs  46  may also facilitate providing that the amount of axial motion imparted by pushrod  42  to load cell  26  can be maintained to within the movement capability of load cell  26 . 
     FIG. 4  is a circuit schematic diagram of an exemplary embodiment the electrical circuit, or conducting paths, integrally fabricated with load cell  26 . Particularly, load cell  26  is fabricated from a metallic substrate with a screen printed thick film pattern of multiple layers. Cell  26  is coated with a corrosion protective coating and including a strain gage bridge, a temperature sensor, and fault protection. The specific metallic substrate selected may depend upon the environment in which cell  26  is to be used. For example, in a gas turbine engine, the typical temperature of the oil at the bearings is about 300 degrees Fahrenheit during running, with a potential for the oil to heat up to about 320 degrees Fahrenheit when the heat exchanger is not operating during shutdown. To compensate for temperature variations, one layer of cell  26  may be a platinum thermocouple. Such load cells are commercially available from Bokam Engineering Inc. 3633 MacArthur Blvd., Suit 412, Santa Ana, Calif. 92704. 
   Cell  26  includes a Wheatstone bridge formed by resistors R 1 , R 2 , R 3 , and R 4 . A voltage signal is supplied to the bridge by a voltage line V coupled to the junction between resistors R 1  and R 2 . Resistors R 3  and R 4  are coupled to a ground line GND. Output signals are provided on lines S 1  and S 2  which are connected to the junctions between resistors R 1 , R 4  and R 2 , R 3 , respectively. Resistor R 5  is connected in series with voltage line V and ground line GND. 
   As is known, and in operation, as the strain on load cell  26  varies, the resistances of resistors R 1 , R 2 , R 3 , and R 4  varies. As a result, if bridge is balanced under no load (or if pre-loaded to a selected force), when other forces act on bridge, bridge becomes unbalanced as indicated by signals on lines S 1  and S 2 . The signals on lines S 1  and S 2  are representative of the force acting on cell  26 . If the forces become excessive and result in breaking the conducting path, or vias, coupled to resistor R 5 , such a condition is indicated by the signals on lines V and GND. Therefore, by monitoring such lines V and GND, a fault condition can be detected. With respect to compensation for varying temperature conditions, and as described above, a layer of cell  26  may be a platinum thermocouple. By connecting such layer to output lines S 1  and S 2 , the signals on lines S 1  and S 2  also are representative of temperature conditions at cell  26 . 
   When coupling cell  26  to the measuring circuit which receives signals on lines S 1  and S 2 , and in coupling cell lines V and GND to a power supply, it may be important to ensure good electrical connections are formed and that such connections can withstand the high temperature operating environment. The measuring circuit and power supply coupled to a load cell in a manner sufficient to withstand the high temperature operating environment in a gas turbine engine are commercially available from Bokam Engineering Inc. 3633 MacArthur Blvd., Suit 412, Santa Ana, Calif. 92704. 
   With respect to load cell  26 , only four external wires (e.g., wires  34 ,  36 ,  38 , and  40 ) may need be coupled to such cell  26 . By having only four external wires with cell  26 , the number of wires required with the present sensor assembly is reduced as compared to the number of wires required with known strain gages. Reducing the number of wires is believed to improve reliability by means of fewer circuits. In addition, with the above described load cell, since temperature compensation is performed within the cell, the requirement for external temperature sensors mounted in the region of the strain gages is believed to be eliminated. Eliminating the need for such external temperature sensors is believed to further simplify installation and operation of the present sensor assembly. 
     FIG. 5  is a schematic block diagram of an exemplary embodiment of sensing circuit  100  for use with assembly  10 . Circuit  100  includes a plurality of sensor assemblies  10  electrically coupled to signal conditioning electronics  102  located off-board the engine (not shown) via a plurality of connectors  104 . Although three assemblies  10  are illustrated, bearing housing may have any number of assemblies  10  secured thereto. In the exemplary embodiment, signal conditioning electronics  102  read a micro strain measurement of each assembly  10  as a voltage. Signal conditioning electronics  102  may include a control panel  106  for generally controlling operation thereof and for reading the voltage measurements. In some embodiments, signal conditioning electronics  102  include a chart  108 , for example mounted thereon or located adjacent to, for converting voltage to strain. Although signal conditioning electronics may have other gains, in some embodiments signal conditioning electronics include a gain of between about twenty to one and about thirty to one. 
   As described above, sensor assembly  10  can be utilized for measuring bearing thrust loads in a gas turbine engine and may be less difficult and/or time-consuming to install in both development and production engines as compared to known strain gage assemblies. For example, because sensor assembly  10  is mounted directly to bearing housing  50  rather than to bearing races, the need for reworking the bearing races to install sensors may be eliminated. Moreover, sensor assembly  10  may be secured to bearing housing  50  without using an adhesive. As such, sensor assembly  10  may facilitate reducing the time and/or costs associated with measuring bearing thrust loads. 
   The assemblies, bearings, and methods described and/or illustrated herein are described and/or illustrated herein in connection with a specific assembly for being secured to a bearing housing of a gas turbine engine. However, it should be understood, that such sensing elements could be used in many alternative securing arrangements. Therefore, the manner of securing the sensing element to the bearing housing is an exemplary configuration and the sensing element could be used in connection with other securing assemblies. 
   Exemplary embodiments of assemblies, bearings, and methods are described and/or illustrated herein in detail. The assemblies, methods, and bearings are not limited to the specific embodiments described and/or illustrated herein, but rather, components of each assembly and bearing, as well as steps of each method, may be utilized independently and separately from other components and/or steps described and/or illustrated herein. Each component and/or step can also be used in combination with other components and/or steps. 
   Each of cleats  22  and/or  24  may be referred to herein as a first and/or a second cleat. Each of anchor members  14  and  16  may be referred to herein as a first and/or a second anchor member. Each of bearing housing openings  72  and/or  74  may be referred to herein as a first and/or a second opening. 
   When introducing elements/components/etc. of the assemblies, bearings, and methods described and/or illustrated herein, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.