Variable Gear Ratio Starter Generator for Aircraft Engines
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Solution Overview
Problem
Gas turbine starter/generators face a contradiction in achieving optimal mechanical operating conditions as a starter versus a generator, with existing gear ratios compromising between high speeds for starting and acceptable generator frequencies, leading to harmful frequency variations.
Innovation Solution
A system with a fixed accessory gearbox and a gearbox with multiple gear ratios, allowing the gear ratio to change based on the mode of operation, prioritizing torque during starting and adapting to generator speeds, using an electronic unit to control the gearbox actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a fixed gear ratio is used between the AGB and starter/generator, then the starter can achieve high speeds of rotation to minimize torque, but the generator experiences a large range of speed variation that increases frequency variation and harms network integration
Solution Approach 1:
The patent applies the dynamics principle by making the gear ratio changeable rather than fixed. A gearbox with variable gear ratios is introduced between the AGB and the starter/generator, allowing the system to adapt the transmission ratio dynamically based on operational requirements. This resolves the contradiction by enabling high gear ratios during starting to minimize torque while maintaining low gear ratios during generation to stabilize frequency and improve network integration.
2Speed
If the gear ratio is optimized for generator mode, then the generator operates at appropriate speeds, but the starter experiences insufficient torque to reliably start the engine
Solution Approach 1:
The variable gear ratio gearbox enables dynamic adaptation of the transmission ratio based on the operational mode. During starting, the system selects higher gear ratios to maximize torque transmission to the engine. During generation, it switches to lower gear ratios to maintain appropriate rotational speeds for stable frequency output. This dynamic adjustment resolves the contradiction between speed optimization for generation and torque optimization for starting.
Data Source
AI summary
A system and a method for controlling an aircraft engine starter/generator. The system includes an AGB of fixed gear ratio for coupling mechanically to a turbine shaft of the engine to enable the engine to be started, a gearbox having multiple gear ratios mechanically coupled to a gearwheel of the AGB, a starter/generator mechanically coupled to a gearwheel of the gearbox, and a controller to cause the gear ratio of the gearbox to be changed as a function of the mode of operation of the starter/generator.