Aircraft Generator Drive With Epicyclic Speed Regulation
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Solution Overview
Problem
Existing turbomachine generator speed control systems, particularly in aircraft, face inefficiencies due to low hydraulic motor efficiency, dissipative losses, and unreliability of hydromechanical differential devices, which struggle to maintain constant speed across varying turbomachine speeds.
Innovation Solution
A purely electrical drive device using first and second electric motors and an epicyclic gear reducer to control the rotation speed of the generator input shaft, ensuring constant output speed without additional power draw from the accessory relay box, eliminating dissipative losses and enhancing reliability through motor redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydromechanical differential device with fixed or variable displacement hydraulic motor is used to control generator speed, then constant speed control can be achieved, but the overall efficiency is low (close to 80%) due to internal leaks, friction, and dissipative losses in the pressure regulator
Solution Approach 1:
The patent replaces the hydromechanical differential device with a purely mechanical differential device consisting of an epicyclic gear reducer with three elements (sun gear, planet carrier, ring gear). This substitution eliminates hydraulic fluid, pumps, motors, and pressure regulators, thereby removing internal leaks, friction losses, and dissipative losses associated with hydraulic systems while maintaining constant speed control capability through mechanical gear ratios.
2Adaptability or versatility
If a hydraulic system with wide speed range operation is used to adjust generator speed, then adaptability to varying turbomachine speeds is improved, but the risk of wear increases and efficiency is affected at low or high speeds
Solution Approach 1:
The patent replaces the hydraulic motor and pressure regulator system with a mechanical epicyclic gear reducer that has inherent mechanical advantage across its operating range. The gear reducer provides smooth torque multiplication and speed reduction through fixed mechanical ratios, eliminating the wear-prone hydraulic components that operate across wide speed ranges, thereby improving reliability while maintaining adaptability.
3Device complexity
If a fixed reduction ratio between accessory gearbox output shaft and generator input shaft is used, then constant speed control is simplified, but the ability to maintain constant frequency at variable turbomachine speeds is compromised
Solution Approach 1:
The patent employs a differential device (epicyclic gear reducer) that dynamically adjusts the effective reduction ratio between the accessory gearbox output and generator input based on the operating conditions. This allows the generator to maintain constant speed and frequency even when the turbomachine speed varies, as the differential mechanism automatically compensates for speed variations through its planetary gear configuration.
4Reliability
If additional power draw from the accessory relay box is permitted to control generator speed, then speed regulation capability is improved, but the mechanical power balance between accessory relay box and generator is disrupted
Solution Approach 1:
The patent replaces the hydraulic power transfer system with a direct mechanical connection through the epicyclic gear reducer. This mechanical differential device redistributes the mechanical power from the accessory relay box output shaft among the three elements (sun gear, planet carrier, ring gear) without requiring additional power draw, maintaining perfect mechanical power balance while enabling precise speed regulation of the generator.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The electrical drive system achieves efficient power transfer, maintains constant generator output speed, and operates reliably across varying turbomachine speeds without the inefficiencies and wear associated with hydraulic systems, ensuring optimal performance and reduced component count.
Implementation Method 1
an epicyclic gear reducer comprising three elements, a central planet gear, an outer ring gear and a planet carrier whose planets mesh with said planet gear and said ring gear
Implementation Method 2
a first electric motor, and control means configured to control said first and second electric motors
Implementation Method 3
said first and second electric motors being arranged to transfer electrical power from one to the other
Data Source
Figure 1~2
Figure 3
Figure 4a~4c
AI summary
The invention relates to a device (20) for driving an integrated generator (16) from an accessories relay box (12) of the turbomachine (10), comprising: - first and second electric motors (30, 40) arranged to transfer electric power from one to the other, - control means for controlling said electric motors, and - an epicyclic reduction gear train (50) comprising a first element intended to be coupled to the accessories relay box, a second element intended to be coupled to the generator, and a third element driven to rotate by said first electric motor (30), and wherein said control means are configured to modify the speed of rotation of the third element in such a way that the second element is driven to rotate at a constant speed.