Civil aircraft APU fire prevention system and fire prevention method thereof

Abstract

The present application relates to the field of civil aviation safety technology, and provides a civil aircraft APU fire prevention system and a fire prevention method thereof, the system comprising an APU, a fire detection assembly, a cockpit alarm module, an ECU electronic control assembly, an LGCIU landing gear control and interface assembly, an automatic fire extinguishing module and a manual fire extinguishing module. The present application can quickly and automatically extinguish fire, eliminating the response delay and uncertainty risk of manual fire extinguishing. At the same time, without adding a special AFECU automatic fire extinguishing controller, the APU fire prevention control can be cooperatively completed by using the existing fire detection assembly, the LGCIU landing gear control and interface assembly and the ECU electronic control assembly configured on the aircraft, and the manual fire extinguishing is guaranteed to be prior by cooperating with a hardware time delay relay, automatic fire extinguishing under ground fire is realized, and the present application has the functions of overheating warning, fault diagnosis and high-reliability redundant fire extinguishing driving capability. The present application can not only reduce the equipment cost, but also improve the safety and reliability of the APU fire prevention system.

Description

Technical Field

[0001] This invention relates to the field of civil aviation safety technology, and in particular to a fire protection system for a civil aircraft APU and its fire protection method. Background Technology

[0002] The Auxiliary Power Unit (APU), a core component in the tail section of an aircraft, houses a small turbine engine and plays a crucial role in supplying the aircraft with electricity and gas. However, due to its involvement with flammable materials and high-temperature heat sources, the APU system inevitably carries a fire risk. Aircraft fires, a major threat to aviation safety, can not only directly lead to equipment damage and flight cancellations, but in extreme cases, can even result in catastrophic crashes and loss of life. Even the smoke generated in the early stages of a fire can pose a serious threat to the lives of those on board, causing severe consequences such as suffocation.

[0003] To address this challenge, modern aircraft are equipped with advanced fire protection systems that provide focused monitoring and protection for multiple high-risk fire areas, including engines, APUs, and cargo holds. Their core value lies in their ability to respond rapidly in the early stages of a fire, effectively containing its spread and maximizing the protection of the aircraft's internal structure and critical equipment from damage, thereby minimizing economic losses and negative impacts.

[0004] Specifically, the APU fire protection system integrates two core functions: fire detection and fire prevention, forming a highly efficient protection mechanism. The fire detectors monitor temperature changes in the APU area in real time. Once the temperature abnormally rises to the warning threshold, it immediately triggers both light and audible alarm signals, alerting the crew to take appropriate measures. Fire prevention is another key function of the system. After a fire is confirmed, the crew must manually activate the fire protection system. At this time, the system will spray extinguishing agent towards the fire source to control the fire.

[0005] While the currently used APU fire protection system can meet the basic fire protection requirements of aircraft, it lacks automatic fire suppression capabilities, and manual fire suppression carries numerous uncertainties. The reasons are as follows: First, the fire extinguisher handle is located inside the aircraft cockpit, an area densely packed with equipment. The cockpit, as the aircraft's command center, is densely packed with various sophisticated instruments, complex buttons, intricate switches, flashing indicator lights, and crucial control handles, making it the primary human-machine interface. In such a complex control environment, responding correctly and quickly to a fire requires operators to possess not only extensive experience but also exceptional composure and judgment. Incorrect operation could lead to equipment damage or even personal injury.

[0006] Second, firefighting personnel must possess the corresponding qualifications and be authorized. This is a prerequisite for entering the aircraft cockpit to perform critical firefighting tasks. Only crew members or professional maintenance personnel who have passed through multiple screening processes and possess solid professional skills are permitted to personally operate the fire extinguisher handle to accurately release the extinguishing agent to quickly contain the fire. Furthermore, even if an individual possesses outstanding skills, they must obtain formal authorization from the airline to ensure the legality and professionalism of performing high-risk tasks.

[0007] Third, the ground work environment is complex and multifaceted. During the pre-flight preparation phase, collaboration among various departments is extremely close, including crew, maintenance, ground services, cleaning, cargo, and security. Frequent personnel movement and complex work arrangements, coupled with external environmental factors, can all create hidden obstacles to early fire identification. When a fire first appears, the noise and variability of the environment often mask subtle signs, increasing the difficulty of identification. Despite interdepartmental collaboration, differences in responsibilities and focuses can lead to delays or misunderstandings in information transmission, hindering timely fire response. Once a complex environment leads to misjudgment or delayed action, it means missing a valuable initial firefighting opportunity, allowing the fire to spread rapidly and pose a serious threat to aircraft and personnel safety.

[0008] It is evident that most existing civil aircraft APU fire suppression systems only support manual fire suppression, which suffers from long response delays and is also subject to limitations imposed by operator qualifications and on-site environment, leading to safety hazards such as misoperation and untimely response.

[0009] In recent years, some civil aircraft have deployed automatic fire suppression systems with APU (Automatic Fire Protection Unit) capabilities. However, these systems require a dedicated AFECU (Automatic Fire Control Unit) for automatic fire suppression, with the entire automatic fire suppression logic handled by this dedicated controller. Adding a dedicated controller increases the number of onboard devices, leading to increased aircraft weight, higher hardware costs, and greater complexity of onboard interfaces. Furthermore, existing APU automatic fire suppression systems use software timing to implement delay logic, making them susceptible to malfunctions such as software crashes or program failures. Therefore, existing APU automatic fire suppression systems are not only structurally complex but also expensive.

[0010] In summary, existing APU automatic fire protection systems cannot reliably guarantee the priority of manual fire extinguishing; traditional fire alarm detection loops generally only identify two states: fire alarm and fault, lacking the ability to provide overheat warnings of fire precursors; and although some fire extinguishing bottles are equipped with double explosion cap redundancy, they lack a completely physically isolated independent drive circuit, leaving room for improvement in redundancy and fault tolerance capabilities. Summary of the Invention

[0011] To address the problems in existing technologies, this invention provides a civil aircraft APU fire protection system and its fire protection method, which can quickly and automatically extinguish fires, thereby completely eliminating the inherent response delay and uncertainty risks of traditional manual fire extinguishing methods. Simultaneously, it eliminates the need for a dedicated AFECU automatic fire extinguishing controller, utilizing existing aircraft-configured fire alarm detection components, LGCIU landing gear control and interface components, and ECU electronic control components to collaboratively complete APU fire protection control. Furthermore, it incorporates hardware time-delay relays to ensure manual fire extinguishing priority, enabling automatic fire extinguishing in ground fire situations. It also features overheat warning, fault diagnosis, and highly reliable redundant fire extinguishing drive capabilities, reducing equipment costs and improving the safety and reliability of the APU fire protection system.

[0012] To achieve the above objectives, a civil aircraft APU fire protection system is provided, comprising an APU, a fire detection component, a cockpit alarm module, an ECU electronic control component, an LGCIU landing gear control and interface component, an automatic fire suppression module, and a manual fire suppression module. The APU includes a fire detection loop module and a fire extinguishing bottle; the fire detection loop module is used to collect the temperature inside the APU compartment and send a real-time signal to the fire detection component based on the ambient temperature inside the APU compartment; the fire extinguishing bottle is used to receive the signal from the automatic fire extinguishing module and automatically extinguish the fire in the APU compartment based on the signal sent by the automatic fire extinguishing module. The fire detection component includes a computing module and a control module. The computing module receives real-time signals from the fire detection loop module of the APU, processes and analyzes these signals, and outputs four operating states of the fire detection loop module: fire alarm state, overheating state, open circuit fault state, and short circuit fault state. The control module receives signals from the computing module and, based on the four different operating states of the fire detection loop module output by the computing module, sends different control signals to the cockpit alarm module and the automatic fire suppression module. The cockpit alarm module is used to send corresponding alarms to the crew based on the control signals sent by the fire alarm detection components; The ECU electronic control unit is the onboard control computer of the APU itself, which is responsible for receiving and processing information from the automatic fire suppression module or the manual fire suppression module; when the ECU electronic control unit receives a fire alarm signal from the automatic fire suppression module or the manual fire suppression module, it outputs control commands to execute the APU shutdown operation; The LGCIU landing gear control and interface component is the core computer of the aircraft landing gear system, which is used to output air-to-ground logic signals to the automatic fire suppression module to indicate whether the aircraft is on the ground or in flight. The automatic fire suppression module includes a signal receiving module, a logic judgment module, a time-delay relay module, an automatic release relay module, and a signal transmitting module. The signal receiving module is the signal input interface for the automatic fire suppression module, used to receive fire alarm signals output by the fire alarm detection component, and simultaneously receive air-to-ground logic signals output by the LGCIU landing gear control and interface components. The logic judgment module performs signal logic judgment; the automatic fire suppression triggering condition is met only when both conditions are met simultaneously: a fire alarm signal from the fire alarm detection component and feedback from the LGCIU landing gear control and interface components indicating the aircraft is on the ground. If the aircraft is in the air, the automatic fire suppression function is prohibited from being triggered. The time-delay relay module is a hardware delay mechanism. The relay has a preset delay duration. After receiving a signal from the logic judgment module indicating that the automatic fire extinguishing trigger condition is met, the delay relay module starts a hardware timer. The delay relay module has a built-in actuation switch, which closes after the timer completes, activating the downstream circuit. The delay is achieved through a hardware delay relay, ensuring that the manual fire extinguishing module always has a higher operation priority throughout the entire delay timer cycle. The automatic release relay module is used to automatically release the relay module after the actuation switch of the delay relay module closes, providing an energized detonation circuit for the fire extinguishing bottle to automatically extinguish the fire in the APU compartment. The signal sending module is the output interface of the automatic fire extinguishing module, used to send a fire alarm signal to the ECU electronic control component.

[0013] In the preferred embodiment, the fire alarm detection loop module includes three fire alarm detectors, respectively located at the APU hatch door, the top of the APU compartment, and the APU exhaust pipe. Each fire alarm detector has a built-in fire alarm pressure switch and a fault pressure switch. The three fire alarm detectors form a detection loop. Under normal conditions, the fire alarm detectors keep the fault pressure switch closed. When the ambient temperature reaches the set point of the fire alarm detector, the gas inside the fire alarm detector expands, causing the fire alarm pressure switch to close and reducing the circuit resistance of the fire alarm detector. When the gas pressure inside the fire alarm detector decreases, the fault pressure switch opens, the detector becomes open-circuited, and the circuit resistance becomes infinite. The fire extinguishing bottle contains a halogenated hydrocarbon extinguishing agent. The fire extinguishing bottle body is equipped with an A explosion cap and a B explosion cap. The A explosion cap and the B explosion cap are each equipped with an independent power supply circuit that is physically isolated from each other, forming a redundant triggering mechanism. When either explosion cap receives a power-on signal, it will detonate, break through the sealing plate of the fire extinguishing bottle mouth, and release the halogenated hydrocarbon extinguishing agent into the APU chamber to extinguish the fire.

[0014] In a preferred embodiment, the automatic release relay module has two physically isolated switches, A and B. Switch A controls the on / off state of the power supply circuit for the A explosion cap of the fire extinguisher, and switch B controls the on / off state of the power supply circuit for the B explosion cap of the fire extinguisher. After the actuation switch of the time delay relay module is closed, the automatic release relay module is energized, and switches A and B close synchronously, providing energizing and detonating circuits for the A explosion cap and the B explosion cap, respectively.

[0015] In the preferred technical solution, the calculation module of the fire alarm detection component is used to receive real-time signals output by three fire alarm detectors, and sense the temperature change and fire situation inside the cabin by collecting the resistance value change of the detection loop; the calculation module analyzes the resistance signal and outputs four different working states of the detection loop: fire alarm state, overheating state, open circuit fault state, and short circuit fault state. The control module receives the detection loop status signal output by the computing module; when a fire alarm or overheating state is detected, it outputs two control signals to trigger the cockpit alarm module and the automatic fire extinguishing module, respectively.

[0016] In a preferred embodiment, the fire alarm detection component also has a reserved access interface for a manual fire extinguishing module, supporting manual intervention by crew members in fire extinguishing operations.

[0017] In a preferred embodiment, the cockpit alarm module includes an audible alarm module and a visual alarm module. After receiving an alarm signal from the fire detection component, the audible alarm module outputs an urgent audible alarm. The visual alarm module correspondingly illuminates the fire alarm light, overheat light, malfunction light, and fire extinguisher release light to visually demonstrate the specific situation of the fire and the status of the fire extinguishing system to the crew.

[0018] In a preferred embodiment, the preset delay duration of the time-delay relay module is 3 seconds.

[0019] Another object of the present invention is to provide a fire protection method for a civil aircraft APU fire protection system, which includes the following steps: Step S1: The signal receiving module of the automatic fire extinguishing module receives the fire alarm signal output by the fire alarm detection component, and at the same time receives the air-to-ground logic grounding signal output by the LGCIU landing gear control and interface component. Step S2: The logic judgment module of the automatic fire suppression module performs a logic judgment; when the fire alarm signal is true and the signal of the LGCIU landing gear control and interface component indicates that the aircraft is in a ground state, it is determined that the automatic fire suppression working logic is met; otherwise, automatic fire suppression is not triggered. Step S3: The time delay relay module is powered on and hardware timing is executed; during the timing delay period, the manual fire extinguishing module maintains priority operation authority; after the timing ends, the built-in actuation switch of the time delay relay module closes, and the downstream circuit is turned on. Step S4: The automatic release relay module is energized, and its internally isolated switches A and B close, connecting the two independent power supply circuits corresponding to the A and B explosion caps. Step S5: The signal sending module sends an APU stop signal to the ECU electronic control unit, and the ECU electronic control unit controls the APU to shut down the engine; Step S6: Explosion caps A and B are energized and detonated, breaking through the sealing plate of the fire extinguishing bottle mouth, releasing the extinguishing agent into the APU chamber, and completing the automatic fire extinguishing operation.

[0020] In the preferred technical solution, the preset delay duration of the time-delay relay module hardware timing is 3 seconds.

[0021] The preferred technical solution is as follows: the manual fire extinguishing module operates as follows: the crew presses the external fire extinguishing switch to directly connect the power supply circuits of the A and B explosion caps; the A or B explosion cap is energized and detonates, breaking through the sealing plate of the fire extinguishing bottle, and the fire extinguishing agent is released into the APU compartment to achieve manual fire extinguishing.

[0022] Compared with the prior art, the beneficial effects of the civil aircraft APU fire protection system and its fire protection method of the present invention are: 1. This invention ensures that even without direct human intervention, a fire in the APU compartment can be quickly and automatically initiated to effectively contain the spread of the fire and ensure the overall safety of the aircraft.

[0023] 2. Traditional manual firefighting methods for APU fires are hampered by numerous unpredictable factors, posing operational challenges and risks. Specifically, even with qualified cockpit personnel, a minimum 20-second time window is required from the initial fire to the implementation of firefighting measures. If personnel are off-board performing other tasks, this response time can extend to one minute, posing a severe challenge to fire control. Furthermore, if the boarding gate lacks necessary boarding stairs or ladders, the time can be extended to three minutes, during which time the fire may have spread rapidly, causing incalculable damage. These time delays and the uncontrollability of the on-site environment undoubtedly increase the uncertainty of firefighting operations, threatening the overall safety of the aircraft.

[0024] In contrast, the automatic fire suppression function for the APU introduced in this invention completely overturns this passive situation. In the event of a sudden fire in the APU, this automatic fire suppression system can respond instantly, without any human intervention. It can activate the fire suppression procedure in a mere 3 seconds, precisely and efficiently releasing the extinguishing agent to the fire source, quickly and thoroughly extinguishing the fire. This design not only greatly shortens the fire suppression response time but also fundamentally eliminates the risks of delays, misjudgments, and operational errors that may exist in manual fire suppression, ensuring the immediacy, accuracy, and effectiveness of fire suppression operations.

[0025] 3. Existing purely manual APU fire suppression systems rely entirely on human intervention for firefighting operations. This is constrained by personnel qualifications, the complex cockpit environment, and ground conditions, resulting in long response times and risks of misoperation and missed firefighting opportunities. Existing solutions with automatic fire suppression capabilities require a dedicated AFECU fire suppression controller, increasing the weight and cost of onboard equipment; most rely on software-based delay logic, which cannot guarantee priority for manual fire suppression in case of software failure; traditional detection loops lack overheat warnings; and the redundancy of fire extinguisher bottle circuits provides insufficient isolation.

[0026] 4. This invention does not require an additional independent AFECU dedicated fire suppression controller. It utilizes the fire alarm detection components, LGCIU landing gear control and interface components, and ECU electronic control components already installed on the aircraft to collaboratively complete the entire fire prevention logic. This eliminates the need for additional dedicated control hardware, reduces the number of airborne devices, and lowers the overall weight, hardware cost, and complexity of airborne interfaces.

[0027] 5. This invention uses a hardware time-delay relay to achieve time delay timing, rather than software timing; even if the software malfunctions or fails, the hardware circuitry still ensures that manual fire extinguishing has a higher operational priority, which meets the high reliability safety requirements for civil aircraft airworthiness.

[0028] 6. A detection loop is formed by setting up fire detectors at three locations. The calculation module can analyze and output four states: fire alarm, overheating, open circuit fault, and short circuit fault. It can not only identify fires that have already occurred, but also output early warnings of overheating fire precursors. At the same time, it can complete the self-diagnosis of faults in the detection loop and provide early warnings of potential hazards.

[0029] 7. The A and B explosion caps of the fire extinguishing bottle are equipped with two physically isolated independent power supply circuits, each controlled by an independent switch inside the automatic release relay module; if the hardware of one circuit fails completely, the other circuit will continue to work without interference, greatly improving the redundancy and reliability of the fire extinguishing execution process.

[0030] 8. Relying on the LGCIU to provide air-to-ground logic signals, automatic fire suppression is only allowed to be activated in ground conditions, and automatic release of fire extinguishing agents is prohibited in the air, thus avoiding the safety risks caused by accidental triggering of automatic fire suppression in the air; at the same time, a complete manual fire suppression channel is maintained, and the crew can manually intervene at any time.

[0031] 9. The automatic fire suppression response can be executed after a preset delay, eliminating the risks of response delay, environmental interference, and human misjudgment caused by manual handling, quickly suppressing the fire in the APU compartment, and protecting the safety of the aircraft and personnel.

[0032] In summary, the APU automatic fire suppression function in this invention, with its automated and intelligent characteristics, constructs an impenetrable firewall for aviation safety. It not only effectively curbs the spread of fire and reduces the potential threat of fire to aircraft and passengers, but also buys valuable time for rescue operations in critical moments, minimizing the damage and losses caused by fire and demonstrating the immense value and far-reaching significance of automatic fire suppression technology. Furthermore, it eliminates the need for a separate dedicated AFECU fire suppression controller, utilizing the existing fire alarm detection components, LGCIU landing gear control and interface components, and ECU electronic control components to collaboratively complete the entire fire prevention logic. This eliminates the need for additional dedicated control hardware, reducing the number of onboard devices, lowering overall aircraft weight, hardware costs, and the complexity of onboard interfaces. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the architecture principle of the civil aircraft APU fire protection system in Example 1.

[0034] Figure 2 This is a schematic diagram of the APU composition of the civil aircraft APU fire protection system in Example 1.

[0035] Figure 3 This is a schematic diagram of the fire alarm detection component in Example 1.

[0036] Figure 4 This is a schematic diagram of the cockpit alarm components in Example 1.

[0037] Figure 5 This is a schematic diagram of the architecture of the automatic fire extinguishing module in Example 1. Detailed Implementation

[0038] The relevant terms used in this invention are explained as follows: APU: Auxiliary Power Unit; ECU: Engine Control Unit, the electronic control unit for aircraft engines; LGCIU: Landing Gear Control and Interface Unit.

[0039] Example 1 like Figures 1 to 5 As shown, the civil aircraft APU fire protection system consists of an APU, fire detection components, cockpit alarms, ECU electronic control components, LGCIU landing gear control and interface components, automatic fire suppression, and manual fire suppression.

[0040] like Figure 2As shown, the APU includes fire detectors and fire extinguishing cylinders. There are three fire detectors, forming a detection loop, located at the hatch, the top of the compartment, and the exhaust pipe, respectively, used to detect high temperatures inside the APU compartment. Each fire detector has a built-in fire alarm pressure switch and a fault pressure switch. Normally, the gas pressure in the sensing circuit of the fire detector keeps the fault pressure switch closed; when the temperature reaches the fire alarm set point, the gas inside the fire detector expands, closing the fire alarm pressure switch and reducing the detector's resistance; when the gas pressure in the sensing circuit of the fire detector decreases, the fault pressure switch opens, opening the fire detector and making its resistance infinite.

[0041] The fire extinguishing bottle contains a halogenated hydrocarbon extinguishing agent. It has two explosive caps, A and B. These caps detonate upon receiving an electrical signal. Detonation breaks the seal at the bottle opening, releasing the extinguishing agent into the APU (Activated Fire Punch Unit) compartment for fire suppression. The A and B explosive caps are designed as a redundancy mechanism, ensuring that if one cap fails to detonate, the other can be triggered.

[0042] like Figure 3 As shown, the fire alarm detection component's calculation module is responsible for receiving real-time signals from all fire alarm detectors. Each detector senses an increase in ambient temperature or the occurrence of a fire by measuring changes in the resistance value of its area. The calculation module quickly processes and analyzes the received resistance values ​​to accurately determine the status of each detection loop, including four states: fire alarm, overheating (approaching ignition point), open circuit (circuit disconnection), and short circuit (abnormal circuit connection).

[0043] The fire detection component control module receives signals from the computing module and issues corresponding control signals based on different status types. In the event of a fire or overheating, the control module simultaneously triggers cockpit alarms and automatic fire suppression, issuing clear instructions to the crew. Furthermore, it provides an interface for manual fire suppression, allowing crew intervention when necessary, further enhancing the flexibility and reliability of the fire suppression system.

[0044] like Figure 4 As shown, when the cockpit alarm module receives an alarm signal from the fire detection component, the audible alarm module immediately activates, emitting a rapid and loud alarm sound to quickly attract the crew's attention. Simultaneously, the visual alarm module illuminates corresponding indicator lights, such as fire alarm lights, overheat lights, malfunction lights, and fire extinguisher release lights, providing a clear visual representation of the fire situation and the status of the fire suppression system to the crew. This dual alarm mechanism ensures the timely transmission and accurate understanding of fire alarm information, giving the crew valuable time to take appropriate action.

[0045] The ECU (Electronic Control Unit) is the control computer of the APU (Automatic Fire Protection Unit) system. It is responsible for receiving and processing signals from automatic and manual fire suppression systems. When the ECU detects a fire alarm signal, it quickly controls the APU to shut down, aiming to cut off potential fire sources or prevent the fire from spreading further through the APU.

[0046] The LGCIU landing gear control and interface assembly is the core computer of the landing gear system, providing air-to-ground logic signals for the fire protection system.

[0047] like Figure 5 As shown, the automatic fire extinguishing module includes a signal receiving module, a logic judgment module, a time delay relay module, an automatic release relay module, and a signal sending module. Among them: (1) Signal receiving module, which serves as the input interface for the automatic fire extinguishing function to interact with the outside world, receives signals from the fire alarm detection component, LGCIU landing gear control and interface component.

[0048] (2) Logic judgment module, which judges and processes the signal. If the aircraft is on fire and the aircraft is on the ground, the automatic fire extinguishing function is triggered.

[0049] (3) The delay relay delay module delays the automatic fire extinguishing function by 3 seconds. The purpose of the delay is to provide higher priority for manual fire extinguishing.

[0050] (4) A time-delay relay actuation switch, which is built into the relay and automatically closes after the delay ends, controlling the on / off state of the downstream circuit.

[0051] (5) Automatic release relay with two built-in switches A and B. Switch A controls the circuit connection to explosion cap A, and switch B controls the circuit connection to explosion cap B.

[0052] (6) Signal transmission module, which serves as the output interface for the automatic fire extinguishing function to interact with the outside world, sends the APU shutdown signal to the ECU electronic control component.

[0053] The automatic fire suppression workflow is as follows: The signal receiving module receives the fire alarm signal from the fire detection component and the grounding signal from the landing gear control and interface component; if the fire alarm signal is true and the aircraft is on the ground, the logic judgment module determines that the automatic fire suppression working logic is met; then the time delay relay is energized, the time delay module executes a 3-second timing task, after the delay ends, the relay's built-in actuation switch closes, and the downstream circuit is energized; after the automatic release relay is energized, the built-in A and B switches close, and the circuits to explosion cap A and explosion cap B are energized; the signal sending module sends the automatic fire suppression signal to the ECU, and the ECU controls the APU to shut down; after receiving the energized signal, the explosion cap will detonate itself, causing the sealing plate of the fire extinguishing bottle to break, allowing the fire extinguishing agent to be released into the APU compartment for fire suppression.

[0054] For manual fire extinguishing, pressing the fire extinguishing switch will cause explosion caps A and B to explode, breaking the sealing plate at the fire extinguishing bottle opening and releasing the extinguishing agent into the APU compartment to extinguish the fire.

[0055] Of course, in this embodiment, the fire extinguishing bottle body has two explosion caps, A and B, corresponding to two explosion cap tripping switches, A and B, of the automatic release relay. In other embodiments, the fire extinguishing bottle body may also have one or more explosion caps, and the corresponding automatic release relay may be a single switch or multiple switches.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fire protection system for a civil aircraft APU, characterized in that: It includes an APU, fire detection components, cockpit alarm module, ECU electronic control components, LGCIU landing gear control and interface components, automatic fire suppression module, and manual fire suppression module; The APU includes a fire detection loop module and a fire extinguishing bottle; the fire detection loop module is used to collect the temperature inside the APU compartment and send a real-time signal to the fire detection component based on the ambient temperature inside the APU compartment; the fire extinguishing bottle is used to receive the signal from the automatic fire extinguishing module and automatically extinguish the fire in the APU compartment based on the signal sent by the automatic fire extinguishing module. The fire detection component includes a computing module and a control module. The computing module receives real-time signals from the fire detection loop module of the APU, processes and analyzes these signals, and outputs four operating states of the fire detection loop module: fire alarm state, overheating state, open circuit fault state, and short circuit fault state. The control module receives signals from the computing module and, based on the four different operating states of the fire detection loop module output by the computing module, sends different control signals to the cockpit alarm module and the automatic fire suppression module. The cockpit alarm module is used to send corresponding alarms to the crew based on the control signals sent by the fire alarm detection components; The ECU electronic control unit is the onboard control computer of the APU itself, which is responsible for receiving and processing information from the automatic fire suppression module or the manual fire suppression module; when the ECU electronic control unit receives a fire alarm signal from the automatic fire suppression module or the manual fire suppression module, it outputs control commands to execute the APU shutdown operation; The LGCIU landing gear control and interface component is the core computer of the aircraft landing gear system, which is used to output air-to-ground logic signals to the automatic fire suppression module to indicate whether the aircraft is on the ground or in flight. The automatic fire suppression module includes a signal receiving module, a logic judgment module, a time delay relay module, an automatic release relay module, and a signal transmitting module. The signal receiving module is the signal input interface of the automatic fire suppression module, used to receive the fire alarm signal output by the fire alarm detection component, and simultaneously receive the air-to-ground logic signal output by the LGCIU landing gear control and interface components. The logic judgment module is used to perform signal logic judgment. The automatic fire suppression triggering condition is determined to be met only when both conditions are met: the fire alarm signal sent by the fire alarm detection component and the feedback from the LGCIU landing gear control and interface components indicating that the aircraft is on the ground. If the aircraft is in the air, the automatic fire suppression function is prohibited from being triggered; the time delay relay module is a hardware time delay relay with a preset delay duration. After receiving a signal from the logic judgment module indicating that the automatic fire extinguishing trigger condition is met, the time-delay relay module begins hardware timing. The time-delay relay module has a built-in actuation switch; after timing is complete, the actuation switch closes, activating the downstream circuit. Relying on the hardware time-delay relay to achieve the delay, the manual fire extinguishing module always has a higher operation priority throughout the entire delay timing cycle. The automatic release relay module is used to automatically release the relay module after the actuation switch of the time-delay relay module closes, providing an energized detonation circuit for the fire extinguishing bottle, thus automatically extinguishing the fire in the APU compartment. The signal sending module is the output interface of the automatic fire extinguishing module, used to send fire alarm signals to the ECU electronic control components.

2. The civil aircraft APU fire protection system according to claim 1, characterized in that: The fire alarm detection loop module includes three fire alarm detectors, respectively located at the APU hatch, the top of the APU compartment, and the APU exhaust pipe. Each fire alarm detector has a built-in fire alarm pressure switch and a fault pressure switch. The three fire alarm detectors form a detection loop. Under normal conditions, the fire alarm detectors keep the fault pressure switch closed. When the ambient temperature reaches the set point of the fire alarm detector, the gas inside the fire alarm detector expands, causing the fire alarm pressure switch to close and reducing the circuit resistance of the fire alarm detector. When the gas pressure inside the fire alarm detector drops, the fault pressure switch opens, the detector becomes open-circuited, and the circuit resistance becomes infinite. The fire extinguishing bottle contains a halogenated hydrocarbon extinguishing agent. The fire extinguishing bottle body is equipped with an A explosion cap and a B explosion cap. The A explosion cap and the B explosion cap are each equipped with an independent power supply circuit that is physically isolated from each other, forming a redundant triggering mechanism. When either explosion cap receives a power-on signal, it will detonate, break through the sealing plate of the fire extinguishing bottle mouth, and release the halogenated hydrocarbon extinguishing agent into the APU chamber to extinguish the fire.

3. The civil aircraft APU fire protection system according to claim 2, characterized in that: The automatic release relay module has two physically isolated switches, A and B. Switch A controls the on / off state of the power supply circuit for the A explosion cap of the fire extinguisher, and switch B controls the on / off state of the power supply circuit for the B explosion cap of the fire extinguisher. When the actuation switch of the time delay relay module is closed, the automatic release relay module is energized, and switches A and B close synchronously, providing energizing and detonating circuits for the A explosion cap and the B explosion cap, respectively.

4. A civil aircraft APU fire protection system according to claim 2, characterized in that: The calculation module of the fire alarm detection component is used to receive real-time signals output by three fire alarm detectors, and sense changes in cabin temperature and fire by collecting changes in the resistance value of the detection loop. The calculation module analyzes the resistance signal and outputs four different working states of the detection loop: fire alarm state, overheating state, open circuit fault state, and short circuit fault state. The control module receives the detection loop status signal output by the computing module; when a fire alarm or overheating state is detected, it outputs two control signals to trigger the cockpit alarm module and the automatic fire extinguishing module, respectively.

5. A civil aircraft APU fire protection system according to claim 1, characterized in that: The fire alarm detection component also has a reserved access interface for a manual fire extinguishing module, supporting manual intervention by crew members in fire extinguishing operations.

6. A civil aircraft APU fire protection system according to claim 1, characterized in that: The cockpit alarm module includes an audio alarm module and a light alarm module. After receiving the alarm signal output by the fire detection component, the audio alarm module outputs an urgent audio alarm. The light alarm module correspondingly illuminates the fire alarm light, overheat light, fault light, and fire extinguisher release light to visually demonstrate the specific situation of the fire and the status of the fire extinguishing system to the crew.

7. A civil aircraft APU fire protection system according to claim 1, characterized in that: The preset delay duration of the time-delay relay module is 3 seconds.

8. A fire protection method for a civil aircraft APU fire protection system according to any one of claims 1 to 7, characterized in that: It includes the following steps: Step S1: The signal receiving module of the automatic fire extinguishing module receives the fire alarm signal output by the fire alarm detection component, and at the same time receives the air-to-ground logic grounding signal output by the LGCIU landing gear control and interface component. Step S2: The logic judgment module of the automatic fire suppression module performs a logic judgment; when the fire alarm signal is true and the signal of the LGCIU landing gear control and interface component indicates that the aircraft is in a ground state, it is determined that the automatic fire suppression working logic is met; otherwise, automatic fire suppression is not triggered. Step S3: The time delay relay module is powered on and hardware timing is executed; during the timing delay period, the manual fire extinguishing module maintains priority operation authority; after the timing ends, the built-in actuation switch of the time delay relay module closes, and the downstream circuit is turned on. Step S4: The automatic release relay module is energized, and its internally isolated switches A and B close, connecting the two independent power supply circuits corresponding to the A and B explosion caps. Step S5: The signal sending module sends an APU stop signal to the ECU electronic control unit, and the ECU electronic control unit controls the APU to shut down the engine; Step S6: Explosion caps A and B are energized and detonated, breaking the sealing plate of the fire extinguishing bottle mouth, releasing the extinguishing agent into the APU chamber, and completing the automatic fire extinguishing operation.

9. A fire protection method for a civil aircraft APU fire protection system according to claim 8, characterized in that: The preset delay duration for the hardware timing of the time-delay relay module is 3 seconds.

10. A fire protection method for a civil aircraft APU fire protection system according to claim 8, characterized in that: The manual fire extinguishing module's manual fire extinguishing process is as follows: the crew presses the external fire extinguishing switch to directly connect the power supply circuits of the A and B explosion caps; either the A or B explosion cap is energized and detonates, breaking through the sealing plate of the fire extinguishing bottle, releasing the extinguishing agent into the APU compartment to achieve manual fire extinguishing.

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