Differential Gear Drive Assembly for Variable-Load APU Efficiency
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Solution Overview
Problem
Auxiliary power units in gas turbine engines face efficiency reductions due to varying loads, which move operations away from optimal conditions, and there is a need for improved thermal, transfer, and propulsive efficiencies.
Innovation Solution
A drive assembly incorporating a differential gear system with a ring gear and planet gears, driven by an electric motor and an auxiliary power unit, allows for variable speed adjustment of the output shaft while maintaining a constant speed of the first drive shaft over a predefined range, and includes a generator to provide power to additional motors and compressors, enabling efficient operation across varying loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the auxiliary power unit operates under varying loads, then it can adapt to different power demands, but its operational efficiency decreases as it moves away from optimal operating conditions
Solution Approach 1:
The patent applies dynamics by making the auxiliary power unit's operating speed variable rather than fixed. The control system dynamically adjusts the APU speed to maintain optimal operating conditions across varying load demands, resolving the contradiction between adaptability and efficiency by enabling the system to adapt while staying in its efficient operating range
Solution Approach 2:
The patent changes the operating parameters of the auxiliary power unit by adjusting its rotational speed based on load conditions. The control system modifies the APU speed parameter to maintain peak efficiency across different power demand scenarios, allowing the system to adapt to varying loads without sacrificing operational efficiency
2Loss of energy
If a differential gear system is added to enable variable speed operation, then efficiency is maintained across varying loads, but device complexity increases
Solution Approach 1:
The differential gear system serves multiple functions: it enables variable speed operation to maintain efficiency, transmits power from the APU to the output shaft, and allows for independent control of APU speed versus output speed. This multi-functionality justifies the added complexity by resolving the efficiency-loss contradiction
Solution Approach 2:
The differential gear system acts as an intermediary between the APU and the output shaft, allowing decoupling of their speed relationships. This mediator enables the APU to operate at optimal speed while the output shaft adapts to varying load requirements, resolving the contradiction between maintaining efficiency and adapting to different operating conditions
Data Source
AI summary
A disclosed drive assembly for an auxiliary power unit includes a first drive shaft driven by an auxiliary power unit, a second drive shaft driven by a first electric motor, a differential gear system including a ring gear driven by the second drive shaft, a and planet gears supported within a carrier attached to the ring gear. The first drive shaft and an output shaft are coupled to the planet gears and a generator is driven by the output shaft. The electric motor and the auxiliary power unit combine to drive the output shaft.