# US 11,305,885 B2 · Auxiliary power unit adaptive cooldown cycle system and method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,305,885 B2 - Document ID: US11305885B2 - Status: Granted - Kind: B2 - Application number: 16/244,336 - Filed: 2019-01-10 - Published: 2020-07-16 - Granted: 2022-04-19 - Earliest claimed: 2019-01-10 - Assignees: Honeywell International Inc. - Applicants: Honeywell International Inc. - Inventors: Robert Mallette; Bradley Volkmann - Web page: https://patentgrep.com/patent/US11305885B2 ## CPC - B64D 41/00: Power installations for auxiliary purposes - B64D 33/02: of combustion air intakes - B64D 33/08: of power plant cooling systems - F01D 21/00: Shutting-down of machines or engines, e.g. in emergency; Regulating, controlling, or safety means not otherwise provided for - F01D 21/003: {Arrangements for testing or measuring (for measuring vibrations G01H)} - F02C 7/14: of fluids in the plant {, e.g. lubricant or fuel (F02C7/185 takes precedence)} - F02C 7/32: Arrangement, mounting, or driving, of auxiliaries - 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) - B64D 2033/0213: {specially adapted for auxiliary power units (APU's)} - F05D 2220/50: for auxiliary power units (APU's) - F05D 2260/20: Heat transfer, e.g. cooling - F05D 2270/02: to control rotational speed (n) - F05D 2270/021: to prevent overspeed - F05D 2270/04: to control acceleration (u) - F05D 2270/092: in particular blow-out and relight - F05D 2270/303: Temperature - F05D 2270/3032: excessive temperatures, e.g. caused by overheating - F05D 2270/304: Spool rotational speed - F05D 2270/309: Rate of change of parameters - F05D 2270/44: active, predictive, or anticipative - B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT - 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) - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS ## Abstract A system and method for adaptively controlling a cooldown cycle of an auxiliary power unit (APU) that is operating and rotating at a rotational speed includes reducing the rotational speed of the APU to a predetermined cooldown speed magnitude that ensures combustor inlet temperature has reached a predetermined temperature value, determining, based on one or more of operational parameters of the APU, when a lean blowout of the APU is either imminent or has occurred, and when a lean blowout is imminent or has occurred, varying one or more parameters associated with the shutdown/cooldown cycle. ## Claims ### Claim 1 An auxiliary power unit (APU) system, comprising: an APU configured to rotate at a rotational speed; one or more sensors disposed within the APU, each of the one or more sensors configured to sense an operational parameter of the APU and supply a sensor signal representative of the operational parameter; and an APU control unit in operable communication with the APU and coupled to receive the sensor signals from the one or more sensors, the APU control unit further coupled to receive a shutdown signal and configured, in response to the shutdown signal, to: (i) reduce the rotational speed of the APU to a predetermined cooldown speed magnitude that ensures combustor inlet temperature has reached a predetermined temperature value, (ii) determine, based on one or more of the sensor signals, when a lean blowout of the APU has occurred, and (iii) when a lean blowout has occurred, increasing the predetermined cooldown speed magnitude for use in a subsequent shutdown of the APU. ### Claim 2 (depends on 1) The APU system of claim 1, wherein the APU control unit is configured, in response to the shutdown signal, to reduce the rotational speed of the APU at a predetermined rate. ### Claim 3 (depends on 2) The AU system of claim 2, wherein the APU control unit is configured, in response to the shutdown signal, to reduce the rotational speed of the APU at the predetermined rate for a predetermined time period. ### Claim 4 (depends on 1) The APU system, of claim 1, wherein the APU control unit is configured, in response to the shutdown signal, to: reduce the rotational speed of the APU to a predetermined post-shutdown speed value at a first speed reduction rate, and thereafter reduce the rotational speed of the APU to the predetermined cooldown speed magnitude at a second speed reduction rate. ### Claim 5 (depends on 4) The APU system of claim 4, wherein the APU control unit is further configured to selectively adjust one or both of the first and second speed reduction rates. ### Claim 6 (depends on 1) The APU system of claim 1, wherein: the APU control unit includes at least one overspeed trip circuit, the at least one overspeed trip circuit is coupled to receive a speed signal representative of the rotational speed of the APU and is configured to supply an overspeed trip signal when the speed signal indicates the rotational speed of the APU has exceeded a threshold speed; the APU control unit is further configured to supply a speed signal that indicates the rotational speed of the APU has exceeded the threshold speed to the at least one overspeed trip circuit when the rotational speed of the APU is reduced to the predetermined cooldown speed magnitude; and the overspeed trip signal causes fuel flow to the APU to cease. ### Claim 7 (depends on 6) The APU system of claim 6, wherein: the APU control unit includes a plurality of overspeed trip circuits; and the APU control unit is further configured to supply the speed signal that indicates the rotational speed of the APU has exceeded the threshold speed to a different one of the plurality of overspeed trip circuits each time it receives the shutdown signal. ### Claim 8 (depends on 1) The APU system of claim 1, wherein the APU control unit is further configured to: determine a rate of change of the rotational speed of the APU; and determine that the lean blowout of the APU has occurred when the rate of change of the rotational speed of the APU is greater than a predetermined rate magnitude. ### Claim 9 (depends on 1) The APU system of claim 1, wherein the APU control unit is further configured, upon occurrence of the lean blowout of the APU, to: determine a lean blowout speed, the lean blowout speed being the rotational speed of the APU when the lean blowout occurred; and increase the predetermined cooldown speed magnitude to greater than the lean blowout speed.