Remote APU Start Circuit with Latching Relay
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Solution Overview
Problem
Existing engine starting circuits for auxiliary power units (APUs) on aircraft and other vehicles do not allow for remote startup, especially in cold and dark conditions, posing challenges for efficient and safe power initiation.
Innovation Solution
A circuit comprising a momentary switch, a latching relay, a bi-polar relay, and an unlatching relay that couples an auxiliary power unit to a hot battery for remote activation and switches to a main power bus upon APU startup, enabling remote startup via an exterior control and ensuring safe power transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If existing engine starting circuits are used, then the APU can be started, but remote startup is not enabled especially in cold and dark conditions
Solution Approach 1:
The system performs preliminary actions by maintaining a hot battery bus in standby mode with sufficient power capacity before remote startup is needed. This allows the exterior remote start switch and associated circuits to be immediately operational without requiring the main battery switch to be on or the aircraft to be powered up, enabling startup in cold and dark conditions.
Solution Approach 2:
A latching relay is introduced as an intermediary component between the momentary remote start switch and the APU starting system. The latching relay maintains the circuit closure state after the momentary switch is released, providing sustained power delivery for the starting motor without requiring continuous operator input or the main battery system to be active.
2Ease of operation
If a hot battery bus is used to power remote start circuits, then remote startup is enabled, but power source management becomes complex
Solution Approach 1:
The system employs self-service mechanisms through automatic relay switching. When the APU starts successfully and the alternator begins generating power, the system automatically detects this condition and switches the power source from the hot battery bus to the main battery bus or aircraft electrical system, eliminating the need for manual power source management by the operator.
Solution Approach 2:
The system incorporates feedback mechanisms that monitor the operational state of the APU and the availability of main power. Based on this feedback, control circuits automatically manage the power source transitions, switching from the hot battery bus during startup to the main battery bus when the APU is running and main power is available, thereby simplifying power source management despite the presence of multiple power paths.
3Adaptability or versatility
If the main battery switch is required to be on for APU start, then power management is simplified, but remote startup from exterior is not possible
Solution Approach 1:
The electrical system is segmented into independent functional modules: a hot battery bus for remote startup operations, a main battery bus for normal aircraft operations, and a latching relay circuit for coordinating between them. This segmentation allows the remote startup function to operate independently without requiring the main battery switch to be on, while maintaining separate power management paths that reduce overall system complexity.
Data Source
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AI summary
A circuit and methods for remote auxiliary power unit startup (324) are presented. A first node (320) is coupled to a ground (318) by action of a momentary switch (302) to initiate an activation, and the first node (320) is coupled to the ground (318) by action of a latching relay (304) in response to the activation. An auxiliary power unit (314) is coupled to a hot battery (310) by action of a bi-polar relay (306) in response to the activation.