Aircraft Generator Drive With Epicyclic Speed Regulation
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Solution Overview
Problem
Existing turbomachine systems with hydromechanical differential devices for regulating the speed of integrated generators suffer from low efficiency, significant dissipative losses, and unreliability due to internal leaks, friction, and pressure losses, especially when operating over a wide speed range.
Innovation Solution
A device comprising first and second electric motors and an epicyclic reduction gear train, with control means to adjust the rotational speed of the third element, allowing for constant speed regulation of the generator input shaft, eliminating dissipative losses and providing redundancy for reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hydromechanical differential device with fixed or variable displacement hydraulic motor is used to control generator speed, then the generator can operate at constant speed, but the overall efficiency is low (close to 80%) due to internal leaks, friction, and pressure losses
Solution Approach 1:
The patent replaces the hydromechanical differential device with an electrical differential device comprising two electric motors (first and second electric motors) and control means. The first electric motor is coupled to the accessory gear box and the second electric motor is coupled to the generator, with control means adjusting the speed of the first electric motor to maintain constant generator speed. This substitution eliminates hydraulic fluid, pressure regulators, and dissipative losses associated with hydraulic systems, achieving efficiencies exceeding 90% while maintaining constant speed operation.
2Speed
If a pressure regulator is used to control the speed of the fixed displacement hydraulic motor, then the generator speed can be maintained, but dissipative losses occur at the pressure regulator
Solution Approach 1:
The control means in the electrical differential device replaces the dissipative pressure regulator by directly controlling the rotational speed of the first electric motor through electrical signals. This eliminates the need for pressure regulation mechanisms and associated dissipative losses, as the control means adjusts motor speed electronically without mechanical friction or heat generation from pressure drops.
3Adaptability or versatility
If the hydraulic system operates over a wide speed range, then the generator can adapt to variable turbomachine speeds, but the risk of wear is greater and efficiencies are affected at low or high speeds
Solution Approach 1:
The electrical differential device replaces the hydraulic system with two electric motors and control means, eliminating hydraulic fluid and associated wear from seals, hoses, and pressure regulators. Electric motors can operate reliably across wide speed ranges without the wear and efficiency degradation that plagues hydraulic systems at extreme speeds, as they have no fluid dynamics-related wear mechanisms.
4Device complexity
If a fixed displacement hydraulic motor is used, then the structure is simpler, but the efficiency is low due to internal leaks and friction
Solution Approach 1:
The patent replaces the fixed displacement hydraulic motor with an electrical motor system comprising a first electric motor coupled to the accessory gear box and a second electric motor coupled to the generator. The control means adjusts the speed of the first electric motor to maintain constant generator speed. This electrical substitution eliminates internal hydraulic leaks and friction losses while maintaining structural simplicity through direct electrical coupling and electronic control.
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 solution achieves efficient and reliable speed regulation of the turbomachine generator, maintaining constant output speed without additional power draw from the accessory gear box, with improved efficiency and reduced wear, and allows reversible operation without efficiency penalties.
Implementation Method 1
an epicyclic reduction gear train comprising three elements, a central planetary gear, an external ring gear and a planet carrier whose planet gears mesh with said planetary gear and said ring gear
Implementation Method 2
first and second electric motors, control means configured to control said first and second electric motors, said first and second electric motors being arranged to transfer electrical power from one to the other
Data Source
AI summary
A device for driving an integrated generator from an accessories relay box of a turbomachine. The device includes first and second electric motors arranged to transfer electric power from one to the other, one or more controllers configured for controlling said electric motors, and an epicyclic reduction gear train. The gear train includes 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. The 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.