# US 2024/0200467 A1 · Gearboxes for aircraft gas turbine engines > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2024/0200467 A1 - Document ID: US20240200467A1 - Status: Published application - Kind: A1 - Application number: 18/588,409 - Filed: 2024-02-27 - Published: 2024-06-20 - Earliest claimed: 2020-04-06 - Assignees: ROLLS-ROYCE plc - Applicants: ROLLS-ROYCE plc - Inventors: Mark SPRUCE - Web page: https://patentgrep.com/patent/US20240200467A1 ## CPC - F01D 15/12: Combinations with mechanical gearing (driven by multiple engines F01D13/00) - F01D 25/18: Lubricating arrangements (of machines or engines in general F01M) - F01D 25/166: {Sliding contact bearing (gas bearings F01D25/22)} - F01D 25/186: {for sliding contact bearing} - F02C 3/113: with variable power transmission between rotors - F02C 7/06: Arrangements of bearings (bearings F16C); Lubricating ({of turbo machines F01D25/18; of machines or} engines in general F01M) - F02C 7/36: Power transmission arrangements between the different shafts of the gas turbine plant, or between the gas-turbine plant and the power user ({F02C3/107 - F02C3/13 and} F02C7/32 take precedence; couplings for transmitting rotation F16D; gearing in general F16H) - F02K 3/06: with front fan - F16H 57/0469: {Bearings or seals} - F16H 57/0479: {Gears or bearings on planet carriers} - F05D 2220/323: for aircraft propulsion, e.g. jet engines - F05D 2220/36: specially adapted for the fan of turbofan engines - F05D 2240/54: Radial bearings - F05D 2260/40311: of the epicyclical, planetary or differential type - F05D 2260/98: Lubrication - F16H 1/28: with gears having orbital motion - F16H 2057/085: {Bearings for orbital gears} - Y02T 50/60: Efficient propulsion technologies, e.g. for 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) - F02K: JET-PROPULSION PLANTS (features of jet-propulsion plants common to gas-turbine plants, air intakes or fuel supply control of air-breathing jet-propulsion plants F02C7/00, F02C9/00) - F16H: GEARING - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract Gearboxes for aircraft gas turbine engines, in particular to arrangements for journal bearings such gearboxes, and to related methods of operating such gearboxes and gas turbine engines. Example embodiments include a gearbox for an aircraft gas turbine engine, the gearbox including: a sun gear; a plurality of planet gears surrounding and engaged with the sun gear; and a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin. ## Claims ### Claim 1 A gas turbine engine for an aircraft, comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising: a sun gear; a plurality of planet gears surrounding and engaged with the sun gear; and a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin, wherein: a ratio of a length, L, of the internal and external sliding surfaces to a diameter, D, of each journal bearing is greater than 0.5; a pitch circle diameter of the ring gear is no greater than 1200 mm; and a diametral clearance of each journal bearing, defined by the difference between the diameter of the internal sliding on the planet gear and the diameter of the external sliding surface on the pin, is between around 120 m and around 600 m. ### Claim 2 (depends on 1) The gas turbine engine according to claim 1, wherein a diameter of each journal bearing is between around 120 mm and 200 mm. ### Claim 3 (depends on 1) The gas turbine engine according to claim 1, wherein the internal or external surface of the journal bearing has a surface coating. ### Claim 4 (depends on 3) The gas turbine engine according to claim 3, wherein a thickness of the surface coating is in the range of between 40 micrometers to 200 micrometers. ### Claim 5 (depends on 3) The gas turbine engine according to claim 3, wherein the surface coating comprises a first layer and a second layer, with the first layer being positioned between an underlying material and the second layer. ### Claim 6 (depends on 5) The gas turbine engine according to claim 5, wherein the first layer has a thermal expansion coefficient between that of the underlying material and the second layer. ### Claim 7 (depends on 5) The gas turbine engine according to claim 5, wherein the second layer has a thickness between 50% and 95% f the total thickness of the surface coating. ### Claim 8 (depends on 5) The gas turbine engine according to claim 5, wherein the thickness of the second layer is between 40 and 100 micrometers. ### Claim 9 The gas turbine engine according to 5, wherein the surface coating comprises a third layer positioned such that the second layer is between the first layer and the third layer. ### Claim 10 (depends on 9) The gas turbine engine according to claim 9, wherein the third layer is composed of a material that has a lower hardness than the second layer. ### Claim 11 (depends on 9) The gas turbine engine according to claim 9, wherein: the first layer is between 10 and 20 micrometres in thickness; the second layer between around 40 and 100 micrometres in thickness; and the third layer between around 1 and 15 micrometres in thickness. ### Claim 12 (depends on 1) The gas turbine engine of claim 1, wherein a diameter of the fan is less than 220 cm. ### Claim 13 (depends on 9) The gas turbine engine according to claim 9, wherein: an underlying material on which the surface coating is provided is steel; and/or the first layer is a copper-based alloy; and/or the second layer is copper- or aluminium-based alloy; and/or the third layer is a lead-based alloy. ### Claim 14 (depends on 3) The gas turbine engine of claim 3, wherein: the ratio of the length, L, of the internal and external sliding surfaces to the diameter, D, of each journal bearing is less than 1.4; and/or the ring gear has a pitch circle diameter of 550 mm or greater. ### Claim 15 A gas turbine engine for an aircraft, comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising: a sun gear; a plurality of planet gears surrounding and engaged with the sun gear; and a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin, wherein: a ratio of a length, L, of the internal and external sliding surfaces to a diameter, D, of each journal bearing is greater than 0.5; a pitch circle diameter of the ring gear is no greater than 1200 mm; and a diameter of each journal bearing is between around 120 mm and 200 mm. ### Claim 16 (depends on 15) The gas turbine engine of claim 15, wherein the internal or external surface of the journal bearing has a surface coating. ### Claim 17 (depends on 16) The gas turbine engine according to claim 16, wherein: a thickness of the surface coating is in the range of between 40 micrometers to 200 micrometers; the surface coating comprises a first layer and a second layer, with the first layer being positioned between an underlying material and the second layer; and the second layer has a thickness between 50% and 95% f the total thickness of the surface coating. ### Claim 18 A gas turbine engine for an aircraft, comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising: a sun gear; a plurality of planet gears surrounding and engaged with the sun gear; and a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin, wherein: a ratio of a length, L, of the internal and external sliding surfaces to a diameter, D, of each journal bearing is greater than 0.5; a pitch circle diameter of the ring gear is no greater than 1200 mm; and the internal or external surface of the journal bearing has a surface coating. ### Claim 19 (depends on 18) The gas turbine engine of claim 18, wherein: a diameter of the fan is less than 220 cm; the ratio of a radius of one of the fan blades at a hub to the radius of the fan blade at a tip is in a range of from 0.26 to 0.31; and the gearbox has a gear ratio of 3.1 to 3.5. ### Claim 20 (depends on 18) The gas turbine engine according to claim 18, wherein: the ratio of the length, L, of the internal and external sliding surfaces to the diameter, D, of each journal bearing is less than 1.4; the ring gear has a pitch circle diameter of 550 mm or greater; the ratio of a radius of one of the fan blades at a hub to the radius of the fan blade at a tip is in a range of from 0.26 to 0.31; and the gearbox has a gear ratio of 3 to 3.8.