Low Spool Power Extraction With Variable-Speed Accessory Drive
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Solution Overview
Problem
Gas turbine engines face challenges in managing the wide range of rotational speeds of the low spool, which can be problematic for accessories that require a constant speed, especially with increasing engine bypass ratios and electrical demands.
Innovation Solution
A power extraction system with a variable speed transmission coupled between the low spool transmission and the low spool starter-generator gear, featuring a clutch that can be actuated by a controller based on sensor data, and a gearbox with intermeshed gears that rotate independently of the high spool gear when disengaged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If load is transferred from high spool to low spool for accessory power generation, then fuel consumption decreases and core temperatures reduce, but the wide range of rotational speeds of low spool becomes problematic for accessories requiring constant speed
Solution Approach 1:
A variable speed transmission system is introduced as an intermediary between the low spool and the accessories. This transmission includes a clutch mechanism that can selectively engage or disengage the connection between the low spool starter-generator gear and the high spool gear, allowing the accessories to receive power at a constant speed while the low spool operates at variable speeds to reduce fuel consumption and core temperatures.
2Ease of operation
If a clutch is introduced to engage and disengage low spool to and from high spool, then constant speed can be maintained for accessories, but device complexity increases
Solution Approach 1:
The variable speed transmission system is designed to perform multiple functions: it acts as a speed regulator for accessories requiring constant speed, serves as a clutch mechanism to engage or disengage the low spool from the high spool, and integrates with the existing gear train structure. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity.
3Power
If bypass ratio and electrical needs are increased, then engine performance and power output improve, but demand on compressor section increases
Solution Approach 1:
The power extraction system is segmented into two independent spool systems: a high spool connected to the high pressure compressor and a low spool connected to the low pressure compressor. By transferring accessory power generation to the low spool, the high pressure compressor section is relieved from excessive loading, allowing the engine to accommodate higher bypass ratios and electrical demands without overburdening the compressor section.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A power extraction system (100) for a gas turbine engine (20) may comprise a high spool transmission (72), a low spool transmission (74), and an accessory gearbox (70). The accessory gearbox (70) may comprise a starter-generator (112), a low spool starter-generator gear (108), a high spool gear (102), and a clutch (116) configured to selectively engage and disengage the low spool starter-generator gear (108) and the high spool gear (102). The low spool starter-generator gear (108) may be configured to transfer torque between the starter-generator (112) and the low spool transmission (74) for accessory power generation. The high spool gear (102) may be configured to transfer torque to the high spool transmission (72) for engine starting. The clutch (116) may be controlled by a variable transmission and may allow accessories to be driven by the low spool (30) after starting.