APU Starter Motor Control for Engine Windmilling Suppression
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Solution Overview
Problem
Aircraft auxiliary power units (APUs) experience windmilling during non-operational stages, leading to unnecessary lubricant circulation, which poses fire safety risks and causes wear and tear, highlighting a need for effective control mechanisms to manage rotational motion.
Innovation Solution
A system comprising an electric starter motor, a circuit element, and a control system that determines windmilling states and applies a modulated DC signal to control the rotational motion of the engine, using the starter motor to counteract windmilling and prevent lubricant circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the APU is left non-operational during certain flight stages, then energy consumption is reduced, but windmilling occurs causing lubricant circulation and fire safety risks
Solution Approach 1:
The system applies a counteracting torque to the windmilling engine by controlling the starter motor to rotate in the opposite direction, thereby preventing the harmful windmilling effect before it can cause lubricant circulation and fire safety issues
Solution Approach 2:
The starter motor, originally designed only for starting the engine, is repurposed to counteract windmilling by applying reverse torque, thereby converting a potential harm (windmilling) into a controlled situation that protects the APU
2Device complexity
If the APU is left non-operational, then operational complexity is reduced, but unnecessary wear and tear occurs due to windmilling
Solution Approach 1:
The control system automatically detects windmilling conditions and activates the starter motor to counteract them, allowing the system to protect itself without requiring additional operational complexity or manual intervention from the pilot
3Object-affected harmful factors
If a starter motor is used to counteract windmilling, then rotational motion is controlled, but additional device complexity is introduced
Solution Approach 1:
The starter motor is made multi-functional by using it both for its original purpose (starting the engine) and for counteracting windmilling, thereby controlling rotational motion without introducing additional hardware complexity
Solution Approach 2:
The control functions for engine starting and windmilling prevention are merged into a single control system that manages the starter motor based on detected operational conditions, reducing overall system complexity
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
Effectively reduces or prevents windmilling, mitigating fire safety risks and wear and tear by controlling rotational motion, ensuring safe operation and extending APU lifespan.
Implementation Method 1
A DC signal is applied to an electric starter motor which is coupled to the engine
Data Source
AI summary
Methods and systems for controlling windmilling in an engine are described. An electric starter motor is coupled to the engine, a circuit element is coupled to the electric starter engine and to a DC signal source, and a control system coupled to the engine and to the circuit element. The control system is configured for: determining whether the engine is in a windmilling state; when the engine is in a windmilling state, commanding the circuit element to apply a DC signal to the electric starter motor; and modulating the DC signal applied to the electric starter motor to control a level of rotational motion of the engine.