Patent Description:
During assembly of complex mechanical systems, such as a gas turbine engine, multiple components are arranged in one or more stacks. For example, components can be arranged on a shaft with an interference fit and be preloaded during assembly with a targeted torque value. The application of torque to the component stack during assembly can be subject to a wide range of variability based on a combination of intrinsic properties of the components as manufactured and characteristics of the components during assembly. The stack load must be sufficient to keep components of the stack in place, but too high of a load may cause components to prematurely fail or sustain damage. Designing components in a stack to meet a large stack load range may result in oversized components that add weight to the overall system, which in the case of a gas turbine engine, could result in increased fuel consumption.

<CIT> discloses a wrenching method, an apparatus wrenching attachment, and a medium storing wrenching torque control program.

According to an aspect of the present invention there is provided a system that includes a memory system configured to store a plurality of instructions and a processing system as claimed in claim <NUM>.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the friction torque ratio can relate a difference between the assembly torque and the initial torque to the angle of turn as scaled by a stiffness of the component stack.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the friction torque ratio can be scaled based on a number of threads per unit distance.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the component stack can be a bearing stack of a gas turbine engine.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the indicator of the stack load can be output with respect to target value.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the memory system and the processing system can be integrated with a torque wrench.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the memory system and the processing system can be integrated in an assembly support system.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the memory system and the processing system can be distributed between a torque wrench and an assembly support system.

According to another aspect of the present invention there is provided a method that includes determining, by a processing system, an initial torque applied to a component stack as claimed in claim <NUM>.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the processing system can be integrated in or distributed between a torque wrench and an assembly support system.

In addition to one or more of the features described above or below, or as an alternative to any of the foregoing embodiments, the calibrated force display can be integrated with the torque wrench, and the load specification can be compared to a stack load that is determined by a processing system based on monitoring the initial torque, the assembly torque, and a turn angle applied to the stack nut.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

<FIG> depicts an example of a component stack <NUM> that can be integrated in an apparatus, such as the gas turbine engine <NUM> of <FIG>. For instance, the component stack <NUM> can be part of the bearing systems <NUM> of <FIG>, such as a bearing stack. In the example of <FIG>, the component stack <NUM> includes a seal <NUM>, a first bearing 212a, a spacer <NUM>, and a second bearing 212b arranged relative to (e.g., radially outward from) a shaft <NUM>. The first bearing 212a includes a first roller/rolling element 213a and a first race 214a, and the second bearing 212b includes a second roller/rolling element 213b and a second race 214b.

During assembly, the components <NUM>-<NUM> can be installed on the shaft <NUM> in the order mentioned above (e.g., left-to-right in <FIG>). For example, the seal <NUM> is installed first, then the first bearing 212a, then the spacer <NUM>, then the second bearing 212b. The arrangement/positioning of components (e.g., the components <NUM>-<NUM>) adjacent to one another about a shaft (e.g., the shaft <NUM>) may be referred to as a "stack" herein. A stack end 224a, which is integrally formed with shaft <NUM>, provides a lip/shoulder for applying a torque to the components <NUM>-<NUM> arranged on the shaft <NUM> relative to a stack nut <NUM>. The stack end 224a can act as a bolt head. The stack nut <NUM> can be rotated on a threaded interface <NUM> to apply a load torque to ensure that the components <NUM>-<NUM> remain properly seated and gaps do not form between the components <NUM>-<NUM> in the component stack <NUM>. While <FIG> depicts one example of a component stack, various arrangements of components are contemplated, such as seals, spacers, oil scoops, etc. Further, other component stack configurations may be any type of bolted joint with targeted torque requirements, such as oil fittings, bolted flanges, and the like.

<FIG> is a block diagram of a system <NUM> that can include an assembly support system <NUM> and a torque wrench <NUM>. The assembly support system <NUM> can include a processing system <NUM>, a memory system <NUM>, an input/output interface <NUM>, and a communication interface <NUM>. The processing system <NUM> can include any type or combination of central processing unit (CPU), including one or more of: a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory system <NUM> may include volatile memory, such as random access memory (RAM), and non-volatile memory, such as Flash memory, read only memory (ROM), and/or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms in a non-transitory form. The input/output interface <NUM> can process data input through a user interface <NUM> and output data to the user interface <NUM>. For example, the user interface <NUM> can include a keyboard, a mouse, a display, a touchscreen, and/or input/output devices. The communication interface <NUM> can establish communication with various systems and/or devices through wired, wireless, and/or fiber optic connections.

In embodiments, the torque wrench <NUM> includes a tool head <NUM>, a wrench body <NUM>, and a handle <NUM>. The torque wrench <NUM> can be implemented as a digital torque wrench with a user interface <NUM> having a display <NUM> and inputs <NUM>. The user interface <NUM> can be coupled to a controller <NUM> disposed on, remotely connected to, or incorporated in the torque wrench <NUM>. The controller <NUM> can include a processing system <NUM>, a memory system <NUM>, and an input/output interface <NUM>. The controller <NUM> can also include a communication interface <NUM> to communicate with other devices, such as the assembly support system <NUM> through communication interface <NUM>.

The processing system <NUM> can include any type or combination of central processing unit (CPU), including one or more of: a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The memory system <NUM> can store data and instructions that are executed by the processing system <NUM>. In embodiments, the memory system <NUM> may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms in a non-transitory form. The input/output interface <NUM> is configured to output information on the display <NUM> and receive input from inputs <NUM>. Further, the input/output interface <NUM> can collect sensor data from the one or more sensors <NUM>. The sensors <NUM> can detect torque (e.g., using one or more torque sensing elements) and angle of turn (e.g., using one or more angle sensing elements) status of the tool head <NUM>.

The tool head <NUM> can be sized to engage with the stack nut <NUM> of <FIG> and apply a torque to the stack nut <NUM>. A user, such as a mechanic, can use the torque wrench <NUM> to apply torque to a component stack, such as the component stack <NUM> of <FIG>. In some embodiments, the torque wrench <NUM> is used in conjunction with the assembly support system <NUM> to determine a stack load to be applied to the component stack <NUM> and monitor progress as the torque wrench <NUM> is used to apply torque to the stack nut <NUM> during assembly of the component stack <NUM>.

Referring now to <FIG> with continued reference to <FIG>, <FIG> is a flow chart illustrating a method <NUM> in accordance with an embodiment. The method <NUM> may be performed, for example, by a user working with the assembly support system <NUM> and/or the torque wrench <NUM> of <FIG>.

At block <NUM>, thread and stiffness information associated with a component stack is determined prior to assembly. For example, a design of the component stack <NUM> can be initially created using modeling and design tools to establish dimensions, materials, thread density, etc. A finite element analysis can be performed on the design to analyze an initial approximate preload to determine tightening and loosening effects experienced in the component stack <NUM> during operation. Operating effects and minimum load requirements can used to define a target stack preload for assembly, with a set tolerance range added to account for tool accuracy/precision. The finite element analysis can also be used to determine stiffness values, such as axial stiffness of one or more joints. Thread and stiffness information can be stored in computer memory, such as the memory system <NUM>. The analysis may be performed by software instructions executed by the assembly support system <NUM> or another system (not depicted). When analysis and computations are performed by another computer system, the results of the analysis and computations can be transmitted to the assembly support system <NUM> and/or the torque wrench <NUM>.

At block <NUM>, the torque wrench <NUM> is calibrated based on the thread and stiffness information associated with the component stack <NUM> prior to assembly. The information can be manually input into the torque wrench <NUM> by a mechanic through user interface <NUM> or transferred in through the communication interface <NUM>.

At block <NUM>, the mechanic can install the stack nut <NUM> on the shaft <NUM>, engaging the threaded interface <NUM>, and apply an initial torque to the stack nut <NUM> of the component stack <NUM> to place components <NUM>-<NUM> of the component stack <NUM> in contact between a stack end 224a and the stack nut <NUM>. The initial torque ensures that gaps are closed between the components <NUM>-<NUM>.

At block <NUM>, the mechanic can apply an assembly torque to the stack nut <NUM> using the torque wrench <NUM> until a calibrated force display (e.g., on display <NUM> integrated with the torque wrench <NUM>) indicates that a load specification has been met. The load specification can be defined based on previous analysis, such as that described with respect to block <NUM>. A stack load can be determined in part by either processing system <NUM>, <NUM> or a combination thereof for comparison with the load specification. The stack load can be based on monitoring the initial torque, the assembly torque, and a turn angle applied to the stack nut <NUM>, as further described with respect to <FIG>.

At block <NUM>, verification can be performed to ensure that no load limits were violated in applying the assembly torque. For example, the torque wrench <NUM> and/or the assembly support system <NUM> can use internal limits and/or flags that are set and automatically checked during installation to prevent assembly abnormalities from entering into the fielded fleet. For instance, if an applied torque exceeds a maximum limit during installation but the torque is then lowered to be within range, a record of the over-torque condition can be captured and reported.

In embodiments, calculating friction during a stack assembly procedure can reduce preload variability. Three assembly variables in stack preloading include initial torque, angle of turn, and friction. The initial torque ensures that stack components are properly seated. The angle of turn is an applied rotation angle for a more controlled stack load. Friction can be an unknown variable that determines load from the initial torque. Calculating friction during the assembly process can allow for real-time feedback about the stack load to a mechanic or monitoring system. By recording an angle of turn and torque data detected by the torque wrench <NUM>, friction can be solved using, for example, equation (<NUM>).

Where K is friction (also referred to as friction torque ratio); TD is number of threads per unit distance (e.g., threads-per-inch); Tf is current torque; Ti is initial torque; θ is angle of turn in degrees; and Ks is stiffness.

Based on equation (<NUM>), the stack load can be computed using, for example, equation (<NUM>) and as further described with respect to <FIG>.

Where F is stack load force; θ is angle of turn in degrees; T is current torque; Ks is stiffness; TD is number of threads per unit distance; and Ti is initial torque.

Referring now to <FIG> with continued reference to <FIG>, <FIG> is a flow chart illustrating a method <NUM> in accordance with an embodiment. The method <NUM> may be performed, for example, using the assembly support system <NUM> and/or the torque wrench <NUM> of <FIG>. The term "processing system" used with respect to <FIG> can indicate either processing system <NUM>, <NUM> or a combination thereof (e.g., processing distributed between torque wrench <NUM> and assembly support system <NUM>).

At block <NUM>, a processing system can be determined an initial torque applied to component stack <NUM>, for example, by a user engaging the torque wrench <NUM> with the stack nut <NUM> on the component stack <NUM>. Torque may be determined by monitoring a torque sensor of the sensors <NUM>.

At block <NUM>, the processing system can determine an assembly torque and an angle of turn applied to the component stack <NUM> by the torque wrench <NUM> after the initial torque is applied.

At block <NUM>, the processing system can determine a friction value associated with the component stack <NUM>. The friction value can be a friction torque ratio based on the initial torque, the assembly torque, and the angle of turn. The friction torque ratio can relate a difference between the assembly torque and the initial torque to the angle of turn as scaled by a stiffness of the component stack <NUM>. The friction torque ratio can be scaled based on a number of threads per unit distance.

At block <NUM>, the processing system can determine a stack load of the component stack <NUM> based on the friction value, the assembly torque, and the angle of turn. The stack load can be determined between a stack end 224a of the component stack <NUM> and a stack nut <NUM>.

At block <NUM>, the processing system can output an indicator of the stack load. The indicator of the stack load can be output with respect to target value. The indicator may be output on display <NUM> and/or user interface <NUM>. The indicator can be set based on a stack load target or a target torque. For example, a user can visually compare the results to a target value or an alternate form of alert can be used, such as a light, audio output, haptic feedback, etc. upon meeting the target.

Technical effects can include reducing the variability in torque preloading to allow for leaner designs and better control over variability when designing and installing hardware. Additionally, in the case where the least controllable input, friction, is found to be outside of an assumed range, the assembly processes disclosed herein can detect and correct for such a condition. With the ability to calculate more assembly parameters on-the-fly, limits can be introduced to prevent unintended installation or over-torque of components.

Claim 1:
A system comprising:
a component stack (<NUM>) of a mechanical system, said stack comprising a plurality of components arranged on a shaft (<NUM>) between a stack end (224a) integrally formed with the shaft (<NUM>) and a stack nut (<NUM>);
a memory system (<NUM>,<NUM>) configured to store a plurality of instructions; and
a processing system (<NUM>,<NUM>) configured to communicate with the memory system (<NUM>,<NUM>) and execute the instructions that result in:
determining an initial torque applied to the component stack wherein the initial torque closes gaps between the components;
determining an assembly torque and an angle of turn applied to the component stack (<NUM>) after the initial torque is applied;
determining a friction value associated with the component stack (<NUM>), wherein the friction value comprises a friction torque ratio based on the initial torque, the assembly torque, and the angle of turn;
determining a stack load of the component stack (<NUM>) based on the friction value, the assembly torque, and the angle of turn, wherein the stack load is determined between the stack end (224a) of the component stack (<NUM>) and the stack nut (<NUM>); and
outputting an indicator of the stack load.