Stiffness-variable aircraft engine bracket, temperature control system and design method thereof

Abstract

The present invention relates to the technical field of aircraft engine components, and more specifically to an aircraft engine bracket with variable stiffness, a temperature control system, and a design method. In order to solve the problem that the natural frequency of existing aircraft engine brackets cannot be adjusted and the resonant frequency cannot be effectively avoided when the risk of resonance occurs, a aircraft engine bracket with variable stiffness and a design method thereof are proposed. The copper core enameled wire provided on the variable stiffness mechanism is energized to increase its ambient temperature, so that the temperature on the shape memory alloy support serving as the variable stiffness mechanism can be monitored in real time by a digital thermometer. Based on the displacement feedback signal of the accessory, the power-on time and current intensity of the copper core enameled wire are adjusted in real time by a programmable power supply in conjunction with a resistance box, thereby realizing active vibration reduction of the aircraft engine accessory system. This transformation process realizes the artificial active regulation of the stiffness of the aircraft engine bracket, and when the risk of resonance occurs, its natural frequency can be changed to effectively avoid the resonance zone.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation engine components, and in particular to an aviation engine bracket with variable stiffness, a temperature control system using the bracket, and a design method thereof. Background Art

[0002] Aircraft engines are the core power source of aircraft flight, as important as the heart in the human body. Engine brackets, crucial connecting components located between the casing and accessories, provide critical support. Changes in their mechanical properties can impact the robust operation of the entire engine. These brackets are complex in structure, contain numerous components, and are constantly exposed to multi-frequency, interactive vibrations. They are highly susceptible to vibration failures and even fatigue damage, which in turn can cause severe vibration throughout the engine, seriously impacting its safe operation.

[0003] Topology optimization is one of the primary methods for achieving lightweight design in aircraft engine brackets. During actual flight, aircraft experience multiple hazardous conditions, such as takeoff and climb. The operating conditions of the engine and its associated bracket are complex and highly variable, making existing technologies unable to meet the requirements for bracket topology optimization under these diverse operating conditions. Furthermore, aircraft engines operate in harsh environments, with a variety of causes of vibration failure, such as rotor imbalance and misalignment. Current aircraft engine brackets cannot effectively suppress the transmission of engine casing vibration to connected accessories, necessitating vibration reduction or isolation measures. However, due to structural and layout limitations of aircraft engine brackets, traditional vibration reduction and isolation measures (such as squeeze film dampers, electromagnetic bearings, and metal-rubber vibration dampers) are not suitable for aircraft engine bracket structures. However, new intelligent materials such as shape memory alloys, piezoelectric ceramics, and low-melting-point alloys can change their internal molecular structure under different external environmental stimuli (such as temperature, pressure, and voltage), resulting in the material assuming different states. Therefore, leveraging these properties, it is possible to consider incorporating these new intelligent materials into aircraft engine bracket design, thereby achieving variable-stiffness aircraft engine bracket design.

[0004] Currently, many researchers have conducted topological optimization on aircraft engine brackets, achieving lightweight results. However, these brackets are typically made of a single material, such as titanium alloy or structural steel. While these materials offer high strength and stability, their internal molecular structure is fixed and cannot be adjusted manually. Consequently, when resonance risk arises, their stiffness cannot be adjusted to avoid resonant frequencies.

[0005] Therefore, it is urgent to propose an aerospace engine bracket and a design method thereof in order to solve the above technical problems. Summary of the Invention

[0006] The purpose of the present invention is to solve the problem that the natural frequency of the existing aircraft engine bracket cannot be adjusted and the resonant frequency cannot be effectively avoided when the risk of resonance occurs. The present invention proposes an aircraft engine bracket with variable stiffness and a design method thereof. The stiffness of the bracket can be actively regulated by changing the ambient temperature. The stiffness of the designed bracket can be actively regulated as the external environment changes, and has different stiffnesses under different working conditions, thereby effectively avoiding the resonant frequency, suppressing the vibration of the aircraft engine casing from being transmitted to the accessories, and realizing intelligent active vibration reduction control of the aircraft engine accessory system.

[0007] To achieve the above object, the present invention provides a technical solution:

[0008] An aircraft engine bracket with variable stiffness, comprising:

[0009] The bottom plate has a frame structure;

[0010] The arc-surface restraining plate is arranged in a concave arc shape relative to the bottom plate, and one end of the arc-surface restraining plate is fixedly connected to the bottom plate frame;

[0011] A variable stiffness mechanism is provided between the other end of the back of the cambered constraint plate and the base plate frame, for actively regulating the stiffness of the aircraft engine bracket.

[0012] A further technical solution of the present invention is: the variable stiffness mechanism includes a shape memory alloy pillar and a copper core enameled wire wound on the shape memory alloy pillar, the copper core enameled wire is energized to adjust the temperature on the shape memory alloy pillar, thereby realizing active control of the variable stiffness of the aircraft engine bracket.

[0013] A further technical solution of the present invention is that the shape memory alloy pillar is fixed between the arc-surface constraint plate and the base plate by transient liquid phase diffusion welding.

[0014] A further technical solution of the present invention is that the shape memory alloy pillar is a nickel-titanium alloy.

[0015] A further technical solution of the present invention is: a heat-insulating sleeve is installed on the shape memory alloy pillar, and hydraulic oil is filled between the copper core enameled wire in the heat-insulating sleeve and the shape memory alloy pillar.

[0016] A further technical solution of the present invention is: the aircraft engine bracket also includes a plurality of titanium alloy pillars, the titanium alloy pillars fixed between the back of the arc-surface constraint plate and the base plate frame are arranged vertically symmetrically; the titanium alloy pillars fixed on the inner side of the base plate frame are arranged in a symmetrical inverted triangle shape.

[0017] A further technical solution of the present invention is: a plurality of first connecting holes are provided at the connection between the base plate frame and one end of the arc surface constraint plate to connect the bracket and the receiver and accessories; a plurality of second connecting holes are provided at the other end of the arc surface constraint plate to connect the bracket and the receiver; a plurality of lugs are also provided at both ends of the base plate frame, and a plurality of third connecting holes are provided at the position of the plurality of lugs and the non-connected end of the base plate frame relative to the arc surface constraint plate to connect the bracket and the accessories, so that the arc surface constraint plate and the receiver are tangent, and the base plate and the accessories are connected.

[0018] A further technical solution of the present invention is that the relative angle between the bottom plate and the arc-surface constraint plate is 26.7°, and the central angle of the arc-surface constraint plate is 18°.

[0019] Another technical solution provided by the present invention is:

[0020] A temperature control system comprises the above-mentioned variable-rigidity aircraft engine bracket, a thermocouple, a programmable power supply, a digital thermometer, and a resistance box; the thermocouple is arranged on the shape memory alloy pillar of the aircraft engine bracket and is used to monitor the temperature changes on the pillar in real time, and its output end is electrically connected to the digital thermometer; the thermocouple, resistance box, and programmable power supply are connected in sequence, and the power-on time and current intensity of the copper-core enameled wire are adjusted in real time by the programmable power supply in conjunction with the resistance box, thereby regulating the temperature on the shape memory alloy pillar.

[0021] Another technical solution provided by the present invention is:

[0022] A method for designing an aircraft engine bracket with variable stiffness includes the following steps:

[0023] Step 1: Establish the initial structure of the bracket based on the relative position relationship between the receiver and accessories. The bracket is a solid, curved structure made of titanium alloy.

[0024] Step 2: Based on the external inertial force diagram of the aircraft engine, select dangerous working conditions on the boundary for force analysis. Distribute the inertial force on the bracket to the bolt holes according to the load distribution principle. Perform strength verification before topology optimization to identify the stress concentration locations of the bracket under various working conditions.

[0025] Step 3: Select the remaining area except the area near the bolt hole as the optimization area, take the maximum flexibility of the bracket as the objective function, perform topology optimization based on the strength verification results, and rebuild the bracket model according to the optimization results;

[0026] Step 4: Perform strength check on the re-established bracket model again under the load in step 2, and replace the two pillars with the largest stress with shape memory alloy materials; wrap enameled wire around these two pillars, connect a resistance box and a programmable DC power supply to change the ambient temperature of the two pillars, the temperature of which can be read in real time by a thermocouple, install a thermal insulation sleeve on the pillar, and reduce heat loss by filling it with hydraulic oil.

[0027] Beneficial effects:

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention proposes an aircraft engine bracket with variable stiffness, in which a variable stiffness mechanism is set between the back of the arc-surface constraint plate and the base frame. By energizing the copper-core enameled wire in the variable stiffness mechanism, the temperature of the shape memory alloy strut in the variable stiffness mechanism is adjusted, and the stiffness of the aircraft engine bracket is actively regulated, which can meet the strength requirements of the aircraft under 17 dangerous working conditions such as landing braking, takeoff climbing, etc.

[0030] (2) The present invention proposes a temperature control system for an aircraft engine bracket with variable stiffness. By energizing the copper core enameled wire provided on the variable stiffness mechanism to increase its ambient temperature, the temperature on the shape memory alloy pillar serving as the variable stiffness mechanism can be monitored in real time by a digital thermometer. Based on the displacement feedback signal of the accessory, the energization time and current intensity of the copper core enameled wire are adjusted in real time by a programmable power supply in conjunction with a resistance box, thereby realizing active vibration reduction of the aircraft engine accessory system. This transformation process realizes the artificial active regulation of the stiffness of the aircraft engine bracket. When the risk of resonance occurs, its natural frequency can be changed to effectively avoid the resonance zone.

[0031] (3) The present invention proposes a design method for an aircraft engine bracket with variable stiffness. The re-established bracket model is strength-checked again under the same load, and the two pillars with the largest stress are replaced with shape memory alloy materials; enameled wire is wrapped around the two pillars, and a resistance box and a programmable DC power supply are connected to change the ambient temperature of the two pillars. The temperature can be read in real time by a thermocouple, and an insulation sleeve is installed on the pillar to reduce heat loss by filling it with hydraulic oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Topology optimization process for aircraft engine brackets;

[0033] Figure 2 (a) is a schematic diagram of the appearance of an aircraft engine bracket with variable stiffness;

[0034] Figure 2 (b) basic dimensions of an aircraft engine bracket with variable stiffness;

[0035] Figure 3 An aircraft engine bracket with variable stiffness and its temperature control module;

[0036] Figure 4 There are two ways to wind the copper core enameled wire on the nickel-titanium shape memory alloy pillar;

[0037] Figure 5 The load and temperature changes applied to the variable stiffness bracket of the aircraft engine;

[0038] Figure 6 is the stress variation curve of the variable stiffness bracket over time;

[0039] Figure 7 (a) Schematic diagram of the integrated model of aircraft engine casing, variable stiffness bracket and accessories;

[0040] Figure 7 (b) is a bolt connection hole between the aircraft engine casing 22 and the variable stiffness bracket 23;

[0041] Figure 7 (c) Aircraft engine accessories 24;

[0042] Figure 8 (a) is the overall displacement cloud diagram of the aircraft engine case-variable stiffness bracket-accessories at 22°C;

[0043] Figure 8 (b) is the overall displacement cloud diagram of the aircraft engine case-variable stiffness bracket-accessories at 150°C;

[0044] Figure 9 (a) is the time history curve of the lower aircraft engine accessories;

[0045] Figure 9 (b) The amplitude-frequency characteristic curves of aircraft engine accessories at different temperatures;

[0046] Figure 9 (c) The maximum displacement of the aircraft engine accessories at 48°C and 99°C when the excitation frequency is swept from 0 to 200 Hz.

[0047] In the figure: 1 to 2 - shape memory alloy pillars; 3 to 6 - titanium alloy pillars; 7 - arc-surface constraint plate; 8 - base plate; 9 to 21 - bolt connection holes; 22 - aircraft engine casing; 23 - aircraft engine variable stiffness bracket; 24 - aircraft engine accessory; 25 - bolt connection holes between aircraft engine casing and variable stiffness bracket; 26 - aircraft engine accessory; 27 to 36 - bolt connection holes between aircraft engine accessory and variable stiffness bracket; 301 - programmable DC power supply; 302 - resistance box; 303 - enameled wire; 304 - thermal insulation sleeve; 305 - digital thermometer; 306 - thermocouple; 307 - hydraulic oil. DETAILED DESCRIPTION

[0048] The present invention will be further described in detail below with reference to specific examples, but these examples do not constitute any limitation to the present invention.

[0049] Example 1

[0050] like Figure 2 As shown, an aircraft engine bracket with variable stiffness includes: a base plate 8 having a frame structure;

[0051] The arc-surface restraining plate 7 is arranged in a concave arc shape relative to the bottom plate 8, and one end thereof is fixedly connected to the frame of the bottom plate 8;

[0052] A variable stiffness mechanism is provided between the other end of the back of the cambered constraint plate 7 and the frame of the base plate 8 for actively regulating the stiffness of the aircraft engine bracket.

[0053] The variable stiffness mechanism includes a shape memory alloy support and a copper core enameled wire 303 wound around the shape memory alloy support. The copper core enameled wire 303 is energized to adjust the temperature of the shape memory alloy support, thereby achieving active control of the variable stiffness of the aircraft engine bracket. Figure 4 shown.

[0054] The shape memory alloy pillar is fixed between the arc surface constraint plate 7 and the bottom plate 8 by transient liquid phase diffusion welding. The material of the shape memory alloy pillar is not limited to nickel titanium alloy.

[0055] To improve heat transfer efficiency and prevent heat loss, a thermal insulation sleeve 304, made of a material such as polyurethane foam, is installed over the nickel-titanium shape memory alloy struts wrapped with copper-core enameled wire 303. Hydraulic oil 307 is filled between the copper-core enameled wire 303 and the shape memory alloy struts. This filling of the thermal insulation sleeve 304 improves heat transfer efficiency between the enameled wire 303 and the nickel-titanium shape memory alloy struts.

[0056] The aircraft engine bracket also includes several titanium alloy struts. These are arranged vertically symmetrically between the back of the curved restraining plate 7 and the frame of the base plate 8. The titanium alloy struts attached to the inner side of the frame of the base plate 8 are arranged in a symmetrical inverted triangle shape. This arrangement of the titanium alloy struts improves the overall support stiffness of the bracket.

[0057] The variable stiffness bracket is bolted between the receiver and the accessory. One side of the curved surface constraint plate 7 is connected to the receiver, and the base plate 8 is connected to the accessory. The specific connection method is as follows: a plurality of first connection holes are provided at the junction of the base plate 8 frame and one end of the curved surface constraint plate 7 to connect the bracket to the receiver and the accessory; a plurality of second connection holes are provided at the other end of the curved surface constraint plate 7 to connect the bracket to the receiver; a plurality of lugs are also provided at both ends of the base plate 8 frame, and a plurality of third connection holes are provided at the positions of the lugs and the base plate 8 frame at the end not connected to the curved surface constraint plate 7 to connect the bracket to the accessory, so that the curved surface constraint plate and the receiver are tangent, and the base plate 8 and the accessory are connected.

[0058] The relative angle between the bottom plate 8 and the arc-surface constraint plate 7 is 26.7°, and the central angle of the arc-surface constraint plate 7 is 18°.

[0059] In order to test the stiffness variation range of the aircraft engine bracket with variable stiffness of the present invention, simulation was carried out in ANSYS, and the stiffness of the bracket was adjusted by changing the ambient temperature. Figure 5 The load shown: the load increases evenly from 0 in 0 to 1 second, at which time the ambient temperature around the bracket remains unchanged; 1 to 2 seconds is the stable stage; the ambient temperature around the bracket decreases evenly in 2 to 3 seconds, at which time the load remains unchanged; 3 to 4 seconds is the stable stage. Figure 6 is the stress curve of the bracket over time. Figure 5 It can be seen that within 2 to 3 seconds, the stress of the stent decreases by approximately 25% due to the change in the ambient temperature around it. This stress reduction process is not a simple linear change, but rather a complex nonlinear trend. This indicates that temperature changes can actively control the stiffness of the stent, thereby reducing stress on the stent and avoiding the occurrence of localized stress concentration.

[0060] Example 2

[0061] like Figure 3As shown, a temperature control system is provided in this embodiment, which uses the variable stiffness aircraft engine bracket in Example 1. The temperature control system also includes a thermocouple 306, a programmable power supply, a digital thermometer 305, and a resistance box 302; the thermocouple 306 is arranged on the shape memory alloy pillar and is used to monitor the temperature changes on the pillar in real time, and its output end is electrically connected to the digital thermometer 305; the thermocouple 306, the resistance box 302, and the programmable power supply are connected in sequence, and the power-on time and current intensity of the copper core enameled wire 303 are adjusted in real time by the programmable power supply in conjunction with the resistance box 302 to regulate the temperature on the shape memory alloy pillar.

[0062] The temperature control system operates as follows: A programmable DC power supply 301 is computer-programmed based on the displacement feedback signal, and in conjunction with a resistor box 302, current is supplied to the copper-core enameled wire 303 attached to the nickel-titanium shape memory alloy struts, effectively regulating the temperature of the struts. Furthermore, the displacement transfer rate of the vibration reduction system is defined as the target for fuzzy-PID control. A real-time closed-loop control experiment is then initiated, with the current intensity and duration of the copper-core enameled wire 303 adjusted in real time based on the relative error between the target and the system feedback. To measure the temperature changes on the nickel-titanium shape memory alloy struts in real time, thermocouples 306 are used, and the readings are obtained using a digital thermometer 305.

[0063] Example 3

[0064] In this embodiment, a method for designing the above-mentioned variable-stiffness aircraft engine bracket is provided, comprising the following steps:

[0065] Step 1: Establish the initial structure of the bracket based on the relative position relationship between the receiver and accessories. The bracket is a solid, curved structure made of titanium alloy.

[0066] Step 2: Based on the external inertial force diagram of the aircraft engine, select dangerous working conditions on the boundary for force analysis. Distribute the inertial force on the bracket to the bolt holes according to the load distribution principle. Perform strength verification before topology optimization to identify the stress concentration locations of the bracket under various working conditions.

[0067] Step 3: Select the remaining area except the area near the bolt hole as the optimization area, take the maximum flexibility of the bracket as the objective function, perform topology optimization based on the strength verification results, and rebuild the bracket model according to the optimization results;

[0068] Step 4: The re-established support model is subjected to strength check again under the load in step 2, and the two pillars with the largest stress are replaced with shape memory alloy materials; enameled wire 303 is wrapped around these two pillars, and a resistance box 302 and a programmable DC power supply 301 are connected to change the ambient temperature of the two pillars. The temperature can be read in real time by a thermocouple 306, and a thermal insulation sleeve 304 is installed on the pillars, and heat loss is reduced by filling them with hydraulic oil 307.

[0069] Example 4

[0070] In order to further verify the variable stiffness aircraft engine bracket and its design method according to the present invention, the present invention conducted the following experimental verification:

[0071] Figure 7 (a) shows an integrated model of an aircraft engine casing, a variable stiffness bracket, and accessories, including a casing 22, a variable stiffness bracket 23, and accessories 24. The aircraft engine casing 22 is a cylinder with a diameter of 1m and a wall thickness of 4mm, made of structural steel, with a mass of 59.29kg. Figure 7 The bolt connection holes in (b) are connected to the bracket. Figure 7 (c) is an aircraft engine accessory, which is connected to the bracket through bolt connection holes 27 to 36. The material is structural steel and the mass is 58.96 kg.

[0072] Since the rotor system inside the aircraft engine will inevitably be affected by imbalance, misalignment and aeroelastic excitation, it will generate severe high-frequency excitation on the aircraft engine casing during operation. These excitations will be transmitted to the aircraft engine accessories through the bracket. If resonance is triggered, it will cause irreversible vibration failure to the engine and even cause the tragedy of aircraft destruction and loss of life. The present invention designs a variable stiffness aircraft engine bracket, which can adjust the stiffness of the bracket by changing the ambient temperature, avoid the resonant frequency, and effectively suppress the vibration on the accessory. In order to further test the vibration suppression effect of the variable stiffness bracket 23 on the aircraft engine accessory 24, a simulation was carried out in ANSYS. By changing the ambient temperature, the maximum displacement curve of the accessory 24 at different temperatures was obtained.

[0073] In order to simulate the effects of imbalance, misalignment and aeroelastic excitation, a sinusoidal excitation F = F0sinωt is applied to points A and B on the casing 22, as shown in Figure 8 The overall displacement cloud diagram of the aircraft engine case-variable stiffness bracket-accessories at 48℃ and 99℃ is shown in Figure 8The cloud diagrams at both temperatures show that the maximum displacement occurs at the edge of the receiver, and the movement of the bracket and accessories is transmitted through the receiver. While the bracket and accessories themselves will experience some deformation, this deformation is negligible compared to the receiver, as they essentially vibrate along with the receiver.

[0074] Since the deformation of the attachment is small, it is necessary to take a point on the attachment to characterize the vibration of the attachment and compare it. Figure 9 (a) is the time history curve of the aircraft engine accessory 24 in the steady state stage at 48℃ and 99℃, which shows a significant difference. The maximum displacement of the accessory at 48℃ is 2.625×10 -6 m, and the maximum displacement of the attachment at 99°C is 1.152×10 -6 m, decreased by 56.1%. This is due to the combined effects of temperature and stress, which activate the shape memory effect of the nickel-titanium shape memory alloy struts. The volume fraction of martensite within the struts gradually decreases, and the crystal structure gradually transforms from martensite to austenite. This transformation also causes a change in the elastic modulus of the nickel-titanium shape memory alloy struts, thereby affecting the displacement of the stent and its accessories.

[0075] In order to further evaluate the vibration reduction effect of the variable stiffness bracket 23 at the resonant frequency, the harmonic response analysis of the integrated model at different temperatures was carried out. Among them: the temperature range is 40℃~99℃, and the excitation frequency range is 0~200Hz. The amplitude-frequency curves at various temperatures are shown in Figure 2. Figure 9 As shown in Figure (b), as the temperature continues to rise, the amplitude of the system's resonance decreases, while the resonant frequency increases. Comparing the amplitude-frequency curves at 48°C and 99°C, the maximum amplitude of vibration decreases by 17.7%, and the resonant frequency decreases from 74.6Hz to 89.1Hz. This effectively avoids the resonant frequency, achieving active vibration reduction and isolation for the aircraft engine accessory system.

[0076] Based on the above experimental verification and analysis, the present invention proposes an aircraft engine bracket with variable stiffness and a design method thereof, which can actively regulate the stiffness of the bracket by changing the ambient temperature. The stiffness of the designed bracket can be actively regulated as the external environment changes, and has different stiffnesses under different working conditions, thereby effectively avoiding the resonant frequency, suppressing the vibration of the aircraft engine casing from being transmitted to the accessories, and realizing intelligent active vibration reduction control of the aircraft engine accessory system.

[0077] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. An aircraft engine bracket with variable stiffness, characterized by: include: The bottom plate has a frame structure; The arc-surface restraining plate is arranged in a concave arc shape relative to the bottom plate, and one end of the arc-surface restraining plate is fixedly connected to the bottom plate frame; A variable stiffness mechanism is provided between the other end of the back of the cambered constraint plate and the base plate frame, for actively regulating the stiffness of the aircraft engine bracket; The variable stiffness mechanism includes a shape memory alloy support and a copper core enameled wire wound around the shape memory alloy support. The copper core enameled wire is energized to adjust the temperature of the shape memory alloy support, thereby achieving active control of the variable stiffness of the aircraft engine bracket. A plurality of first connecting holes are provided at the connection between the base frame and one end of the arc surface constraint plate to connect the bracket and the receiver and accessories; a plurality of second connecting holes are provided at the other end of the arc surface constraint plate to connect the bracket and the receiver; a plurality of lugs are also provided at both ends of the base frame, and a plurality of third connecting holes are provided at the position of the plurality of lugs and the non-connected end of the base frame relative to the arc surface constraint plate to connect the bracket and the accessories, so that the arc surface constraint plate and the receiver are tangent, and the base plate and the accessories are connected.

2. The aircraft engine bracket with variable stiffness according to claim 1, characterized in that: The shape memory alloy pillar is fixed between the arc surface constraint plate and the bottom plate by transient liquid phase diffusion welding.

3. The aircraft engine bracket with variable stiffness according to claim 1, characterized in that: The shape memory alloy pillar is nickel-titanium alloy.

4. The aircraft engine bracket with variable stiffness according to claim 1, characterized in that: A heat-insulating sleeve is installed on the shape memory alloy pillar, and hydraulic oil is filled between the copper core enameled wire in the heat-insulating sleeve and the shape memory alloy pillar.

5. The aircraft engine bracket with variable stiffness according to claim 1, characterized in that: The aero-engine bracket also includes a plurality of titanium alloy struts. The titanium alloy struts fixed between the back of the arc-surface constraint plate and the base frame are arranged vertically symmetrically; the titanium alloy struts fixed on the inner side of the base frame are arranged in a symmetrical inverted triangle shape.

6. The aircraft engine bracket with variable stiffness according to any one of claims 1 to 5, characterized in that: The relative angle between the bottom plate and the arc-surface constraint plate is 26.7°, and the central angle of the arc-surface constraint plate is 18°.

7. A temperature control system, characterized in that: The invention comprises the aircraft engine support with variable stiffness as described in any one of claims 1 to 5, and further comprises a thermocouple, a programmable power supply, a digital thermometer, and a resistance box; the thermocouple is arranged on the shape memory alloy pillar of the aircraft engine support and is used to monitor the temperature change on the pillar in real time, and its output end is electrically connected to the digital thermometer; the thermocouple, the resistance box, and the programmable power supply are connected in sequence, and the power-on time and the current intensity of the copper core enameled wire are adjusted in real time by the programmable power supply in conjunction with the resistance box, thereby regulating the temperature on the shape memory alloy pillar.

8. A method for designing a variable stiffness aircraft engine bracket according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: Step 1: Establish the initial structure of the bracket based on the relative position relationship between the receiver and accessories. The bracket is a solid, curved structure made of titanium alloy. Step 2: Based on the external inertial force diagram of the aircraft engine, select dangerous working conditions on the boundary for force analysis. Distribute the inertial force on the bracket to the bolt holes according to the load distribution principle. Perform strength verification before topology optimization to identify the stress concentration locations of the bracket under various working conditions. Step 3: Select the remaining area except the area near the bolt hole as the optimization area, take the maximum flexibility of the bracket as the objective function, perform topology optimization based on the strength verification results, and rebuild the bracket model according to the optimization results; Step 4: Perform strength check on the re-established bracket model again under the load in step 2, and replace the two pillars with the largest stress with shape memory alloy materials; wrap enameled wire around these two pillars, connect a resistance box and a programmable DC power supply to change the ambient temperature of the two pillars, the temperature of which can be read in real time by a thermocouple, install a thermal insulation sleeve on the pillar, and reduce heat loss by filling it with hydraulic oil.

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