Aircraft APU Control System Speed Compensation
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Solution Overview
Problem
Existing aircraft auxiliary power units (APUs) are oversized to handle shock loads, leading to increased aircraft mass and reduced efficiency due to fixed rotational speeds that do not account for varying ambient conditions such as altitude, air density, and electrical load demands.
Innovation Solution
An APU control system that dynamically adjusts the rotational speed of the APU based on air density, altitude, humidity, and electrical load demands using a processor and memory system to maintain a constant power output, allowing for a smaller, more efficient APU design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the APU is oversized to accommodate shock loads, then the rotational speed stability is improved, but the aircraft mass increases
Solution Approach 1:
The patent implements variable rotational speed operation where the APU dynamically adjusts its speed based on actual load conditions and ambient parameters. The control system allows the APU to operate at reduced speeds during normal conditions while maintaining the capability to handle shock loads, eliminating the need for permanent oversizing. This dynamic adaptation resolves the contradiction by providing rotational speed stability only when needed rather than operating continuously at high speed.
Solution Approach 2:
The control system modifies operational parameters (rotational speed, fuel flow rate) based on real-time sensing of ambient conditions and load demands. By changing these parameters dynamically, the system maintains reliability during shock loads while reducing mass-related penalties during normal operation, as the APU is sized for peak demand but operates efficiently at lower levels.
2Device complexity
If the APU operates at fixed rotational speed, then the control system simplicity is maintained, but the fuel efficiency decreases due to inability to adapt to ambient conditions
Solution Approach 1:
The patent employs a feedback control system that continuously monitors ambient parameters (temperature, pressure, humidity) and APU performance metrics, then adjusts fuel flow and rotational speed accordingly. This closed-loop control optimizes fuel efficiency by adapting to changing conditions while maintaining acceptable control system complexity through automated sensing and adjustment mechanisms.
Solution Approach 2:
The control system automatically adjusts APU operation based on sensed conditions without requiring manual intervention. The system self-regulates fuel flow and rotational speed to optimize efficiency across varying ambient conditions, maintaining simplicity while improving performance through autonomous adaptation.
3Power
If the APU is sized for peak shock loads, then the power output capacity is sufficient, but the efficiency at partial load conditions deteriorates
Solution Approach 1:
The APU operates dynamically at variable speeds matched to actual power demands rather than running continuously at peak capacity. The control system adjusts rotational speed and fuel flow to match load requirements, enabling the APU to maintain high efficiency during partial load operation while retaining sufficient power output capacity when peak demand occurs.
Solution Approach 2:
The system changes operational parameters (rotational speed, fuel-air ratio) based on load conditions to optimize efficiency. During partial load conditions, the APU operates at lower speeds with optimized fuel mixing, maintaining power output capacity availability while significantly improving operational efficiency compared to fixed-speed peak-rated operation.
Data Source
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AI summary
An auxiliary power unit (APU) control system for an aircraft is disclosed. The APU control system includes an APU, one or more processors, and a memory coupled to the one or more processors. The memory stores data comprising a database and program code that, when executed by the one or more processors, causes the APU control system to receive a one or more ambient signals indicative of an air density value and one or more power signals indicative of a specific amount of power generated by the APU. The APU control system may further be configured to determine a variable rotational speed of the APU based on the air density value and instruct the APU to operate at the variable rotational speed. The APU continues to generate the specific amount of power when operating at the variable rotational speed.