# US 9,435,683 B2 · Method to determine inertia in a shaft system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,435,683 B2 - Document ID: US9435683B2 - Status: Granted - Kind: B2 - Application number: 14/871,013 - Filed: 2015-09-30 - Published: 2016-04-28 - Granted: 2016-09-06 - Earliest claimed: 2014-10-22 - Assignees: ROLLS-ROYCE plc - Applicants: Rolls-Royce PLC - Inventors: Marko Bacic - Web page: https://patentgrep.com/patent/US9435683B2 ## CPC - G01H 1/006: {of the rotor of turbo machines} - F01D 5/027: {Arrangements for balancing (for balancing rotating bodies in general F16F15/32; for compensating imbalance G01M1/36)} - F02C 9/28: Regulating systems responsive to plant or ambient parameters, e.g. temperature, pressure, rotor speed (F02C9/30 - F02C9/38, F02C9/44 take precedence) - F02C 9/56: with power transmission control - G01H 13/00: Measuring resonant frequency - G01L 3/04: wherein the torque-transmitting element comprises a torsionally-flexible shaft - G01M 5/0025: {of elongated objects, e.g. pipes, masts, towers or railways (G01M5/0058 takes precedence)} - F05D 2260/80: Diagnostics - F05D 2270/334: Vibration measurements - F05D 2270/335: Output power or torque - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - F01D: NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES (machines or engines for liquids F03; non-positive displacement pumps F04D) - F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00) - G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G) - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS ## Abstract A method to determine inertia of components of a rotating shaft system. The shaft system includes a shaft coupling a turbine to drive the rotation and a load to be driven by the rotation. The method includes steps to: apply a feedback to a forcing input to the shaft system; measure resonant frequency of the shaft; iterate steps 1.a) and 1.b) for different feedbacks; plot resonant frequency squared against gain; and determine inverse of gradient from the plot to give inertia of the turbine. Also a method to determine shaft stiffness using the inertia of the turbine. ## Claims ### Claim 1 A method to determine inertia of components of a rotating shaft system; the shaft system comprising a shaft coupling a turbine to drive the rotation and a load to be driven by the rotation; the method comprising steps to: a) apply a feedback to a forcing input to the shaft system, wherein the feedback comprises a gain; b) measure resonant frequency of the shaft; c) iterate steps a and b for different feedbacks; d) plot resonant frequency squared against gain; and e) determine inverse of gradient from the plot to give inertia of the turbine. ### Claim 2 (depends on 1) A method as claimed in claim 1 wherein the load comprises a fan; a compressor; or a propeller. ### Claim 3 (depends on 1) A method as claimed in claim 1 wherein the forcing input comprises perturbed fuel flow. ### Claim 4 (depends on 1) A method as claimed in claim 1 wherein the feedback comprises a small variation in fuel flow; a movement of variable stator vanes to change the pressure at the exit of the load; a movement of variable nozzle guide vanes; a movement of variable bleed valves to change the load capacity; a movement of a variable area nozzle. ### Claim 5 (depends on 1) A method to determine shaft stiffness in a steady state running condition; the method comprising steps to: a) determine inertia of the turbine according to claim 1; b) identify a local minimum frequency and square it; c) determine resonant frequency of the shaft and square it; d) determine frequency difference by subtracting the square of the local minimum frequency from the square of the resonant frequency; and e) determine shaft stiffness by multiplying the inertia of the turbine by the frequency difference. ### Claim 6 (depends on 5) A method to determine shaft stiffness at an initialisation condition; the method comprising steps to: a) determine shaft stiffness in the steady state running condition preceding initialisation according to claim 5; b) determine steady state resonant frequency in the steady state running condition preceding initialisation; c) determine initialisation resonant frequency in the initialisation condition; d) determine the ratio of resonant frequencies by dividing the square of the initialisation resonant frequency by the square of the steady state resonant frequency; and e) multiply the ratio of resonant frequencies by the steady state shaft stiffness to give the initialisation shaft stiffness. ### Claim 7 (depends on 5) A method to determine shaft torque comprising steps to: a) determine shaft stiffness according to claim 5; b) measure shaft twist angle; and c) multiply together the shaft stiffness and shaft twist angle to give shaft torque. ### Claim 8 (depends on 7) A method to control a gas turbine engine comprising steps to: a) determine shaft torque according to claim 7; b) determine actual shaft power by multiplying together shaft torque and rotational speed of the shaft; c) compare actual shaft power to demanded engine power to give a comparison value; and d) change fuel flow to the gas turbine engine if the comparison value is non-zero. ### Claim 9 (depends on 8) A method as claimed in claim 8 further comprising increasing fuel flow if the comparison value is less than zero or decreasing fuel flow if the comparison value is greater than zero. ### Claim 10 (depends on 1) A controller comprising the method as claimed in claim 1. ### Claim 11 (depends on 1) A gas turbine engine comprising in the method as claimed in claim 1. ### Claim 12 (depends on 10) A gas turbine engine comprising the controller as claimed in claim 10. ### Claim 13 (depends on 11) A gas turbine engine as claimed in claim 11 wherein the shaft is a low pressure shaft, an intermediate pressure shaft or a high pressure shaft. ### Claim 14 (depends on 1) A computer readable medium, having a computer program recorded thereon, wherein the computer program is adapted to make a computer execute the method according to claim 1. ### Claim 15 (depends on 1) A computer program having instructions adapted to carry out the method according to claim 1. ### Claim 16 (depends on 14) A computer program comprising the computer readable medium as claimed in claim 14.