TURBOFAN ENGINE BEARING AND GEARBOX ARRANGEMENT

摘要

A turbofan engine (300; 600; 700) comprising a fan shaft (120) configured to rotate about an axis (500) of the engine. A fan drive gear system (60) is configured to drive the fan shaft. The fan drive gear system has a centerplane (540). A first spool comprises a high pressure turbine (326) and a high pressure compressor (324). A second spool comprises an intermediate pressure turbine (328), a lower pressure compressor, and a shaft (334) coupling the lower pressure turbine to the intermediate pressure compressor. A third spool comprises a lower pressure turbine (330) coupled to the fan drive gear system to drive the fan. The engine has a plurality of main bearings. The turbofan engine has a single stage fan. Of the main bearings, at least one is a shaft engaging bearing engaging a driving shaft (336) coupled to the fan drive gear system. A closest (340; 640) of the shaft engaging bearings engaging the driving shaft behind the fan drive gear system has a centerplane (550) and a characteristic radius (RB). The half angle (θ) of a virtual cone (530) intersecting the core flowpath inboard boundary at the gear system centerplane (540) and said closest of the shaft engaging bearings at the characteristic radius (RB) is greater than about 32°. A hub to tip ratio (HR:FR) of the fan is less than about 0.38.