Gas turbine engine dual towershaft accessory gearbox assembly with a transmission

A gas turbine engine assembly comprising:

• a turbine section having a first turbine and a second turbine, the first and second turbines mounted for rotation about a common rotational axis within an engine static structure;
• a first turbine shaft arranged coaxially with a second turbine shaft, wherein the first turbine is operatively mounted to the first turbine shaft, and the second turbine is operatively mounted to the second turbine shaft;
• a first towershaft coupled to the first turbine shaft and a second towershaft coupled to the second turbine shaft;
• an accessory drive gearbox mounted to the engine static structure, the accessory drive gearbox including a common housing, a first set of gears and a second set of gears arranged within the common housing, the first towershaft extending into the common housing and coupled to the first set of gears, the second towershaft extending into the common housing and coupled to the second set of gears;
• an electric machine;
• and
• a transmission coupling the electric machine to the first set of gears, the transmission transitionable between a first mode where the electric machine is driven at a first speed relative to the first towershaft in operation, and a second mode where the electric machine is driven at a different, second speed relative to the first towershaft in operation;
• and
• wherein the engine static structure includes an intermediate case surrounding a core flow path defined along a compressor section driven by the turbine section, the accessory drive gearbox is mounted to the intermediate case, the intermediate case includes a first strut and a second strut directly circumferentially adjacent to the first strut with respect to the common rotational axis, the first towershaft extends through the first strut, and the second towershaft extends through the second strut;
• wherein the first and second turbine shafts are inner and outer shafts, respectively, and the first and second turbines are low and high pressure turbines, respectively;
• wherein a first set of accessories are configured to be rotationally driven by the first towershaft through the first set of gears, the first set of accessories including the electric machine and an oil pump;
• and
• wherein the oil pump is dedicated to communicate oil to a bearing system including a bearing supporting the first turbine shaft at a position axially forward of the accessory drive gearbox relative to the common rotational axis, and the oil pump is driven at a fixed ration relative to a speed of the first towershaft in both the first second modes.