Aero-Engine Fuel Pump Gear Drive for Generator Integration
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Solution Overview
Problem
Aero-engine fuel pumping systems face challenges in upgrading to electronic control systems due to insufficient drive output pads in older engines, leading to high windage losses when using fuel as a lubricant and the need for gear arrangements that increase resistance and size, especially when integrating a permanent magnet alternator for power generation.
Innovation Solution
A fuel pumping system design featuring a high pressure pump with a drive gear, idler gear, and output gear, where the output gear drives an electrical generator rotor and the idler gear drives a low pressure pump rotor, all submerged in fuel for lubrication, allowing for smaller gear diameters and reduced windage losses, enabling the generator to operate at higher speeds without dedicated drive pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gear arrangement is fully submerged in fuel for lubrication, then safe lubrication is achieved, but windage losses increase significantly due to fuel density
Solution Approach 1:
The patent changes the physical state of the lubrication system by introducing a fuel/air mist instead of submerging gears in liquid fuel. This parameter change reduces the density of the lubricating medium from approximately 1000 times that of air (liquid fuel) to a much lower density mist, thereby reducing windage losses while maintaining lubrication effectiveness.
Solution Approach 2:
The patent employs a pneumatic approach by using compressed air to generate a fuel/air mist for lubrication. The compressed air system atomizes fuel and delivers it to the gear arrangement, replacing the hydraulic approach of submerging gears in liquid fuel. This pneumatic lubrication system achieves safe lubrication with minimal windage losses.
2Adaptability or versatility
If large diameter gears are used to straddle the spacing between axes of rotation, then the HP pumping stage and PMA can be installed, but windage losses increase due to larger gear surface area
Solution Approach 1:
The patent changes the lubrication medium from liquid fuel to fuel/air mist, which dramatically reduces the density and thus the windage losses. This parameter change allows the system to tolerate larger gear diameters needed for installation spacing, as the reduced density of the mist minimizes the energy penalty for rotating larger gears.
3Adaptability or versatility
If an electrical generator is added to the accessory gear box without a dedicated drive output pad, then the generator can be integrated, but the generator must share a drive pad with other components
Solution Approach 1:
The patent segments the drive system by introducing an idler gear that separates the drive functions. The idler gear allows the accessory gear box to drive multiple components (HP pump, LP pump, and generator) independently from a single drive pad, effectively segmenting the power transmission paths without requiring multiple dedicated drive pads.
Solution Approach 2:
The idler gear acts as an intermediary element in the drive train. It mediates between the drive gear and the output gear, allowing the generator to be driven at a different speed than the HP pump while sharing the same drive pad. This intermediary gear enables flexible speed ratios and component integration without increasing drive pad requirements.
4Weight of moving object
If the generator is driven at higher speeds using a gear arrangement, then a smaller, lighter generator can be used, but the gear arrangement increases windage losses when submerged in fuel
Solution Approach 1:
The patent uses a pneumatic fuel/air mist lubrication system instead of liquid fuel submersion. This allows the gear arrangement to rotate at higher speeds with minimal windage losses, enabling the generator to be driven at higher speeds and thus allowing the use of a smaller, lighter generator unit.
Data Source
AI summary
A fuel pumping system comprises a high pressure pump having a drive input, a drive gear driven for rotation, in use, by the drive input, an idler gear driven by the drive gear, and an output gear driven by the idler gear, wherein the output gear is arranged to drive a rotor of an electrical generator and the idler gear is arranged to drive a rotor of a low pressure pump.