Rail transit locomotive shell, control system, control method and manufacturing method

Abstract

The application discloses a rail transit vehicle head shell, a control system, a control method and a manufacturing method, and relates to the technical field of rail transit vehicle structures. The vehicle head shell comprises an outer skin, an electrically variable stiffness core layer and an inner skin, forming a sandwich structure. The electrically variable stiffness core layer generates Joule heat when the conductive network is electrified, reducing the stiffness of the core layer. After power-off, the temperature decreases and the stiffness of the core layer is restored. The control system comprises a vehicle speed sensor, a strain sensor, a temperature sensor, a controller and a partition power supply unit. The control method comprises Kalman filter fusion of multi-source sensing data, target stiffness mapping and driving voltage calculation, vehicle speed grading adaptive variable stiffness control, partition pulse width modulation driving output, closed-loop regulation and over-temperature protection, and fault safety response. The manufacturing method adopts a single-face negative mold vacuum introduction integrated forming process. The application solves the problem that the existing rail transit vehicle head shell has a fixed stiffness structure and cannot be adaptively adjusted according to operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of rail transit vehicle structure technology, specifically relating to a rail transit vehicle head shell and control system, control method and manufacturing method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] There is a fundamental contradiction in the structural performance requirements of the train head shell for rail transit vehicles at different operating speeds: at low speeds, frequent starts and stops and complex track excitation necessitate a lower stiffness in the head shell to absorb vibrations and improve passenger comfort; at high speeds, aerodynamic loads increase significantly, requiring a higher stiffness in the head shell to ensure aerodynamic stability and structural safety. Currently, rail transit head shells generally employ fixed-stiffness structures made of carbon fiber reinforced resin composite materials. This stiffness is fixed after manufacturing and cannot be adaptively adjusted according to operating conditions, making it difficult to simultaneously meet the dual requirements of low-speed vibration absorption and high-speed load bearing.

[0004] Existing intelligent variable stiffness technologies mainly include magnetorheological elastomers, piezoelectric materials, and shape memory polymers. Magnetorheological elastomers require a continuous external magnetic field, resulting in complex and energy-intensive auxiliary electromagnetic systems; piezoelectric materials have high driving voltages and small available strain, making it difficult to achieve macroscopic stiffness adjustment for large-scale structures; traditional thermally driven shape memory polymers typically require tens of minutes to respond and are difficult to integrate with the manufacturing processes of complex curved vehicle front shells. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a rail transit car head shell and its control system, control method, and manufacturing method, which solves the problem that existing rail transit car head shells are fixed-rigidity structures, whose stiffness remains unchanged after manufacturing and cannot be adaptively adjusted according to operating conditions.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a front housing for a rail transit vehicle, comprising: an outer skin made of carbon fiber reinforced resin composite material; an electrostrictive stiffness core layer disposed on the inner side of the outer skin, the electrostrictive stiffness core layer being composed of a shape memory polymer matrix and a conductive network embedded in the shape memory polymer matrix, the conductive network being connected to an external power supply circuit; and an inner skin stacked on the inner side of the electrostrictive stiffness core layer, the inner skin being made of fiber reinforced resin composite material. The outer skin, the electrochromic stiffness core layer, and the inner skin form a three-layer sandwich structure. When the conductive network is energized, it generates Joule heating, which raises the temperature of the shape memory polymer matrix above the glass transition temperature, and the stiffness of the electrochromic stiffness core layer decreases. When the power is turned off, the temperature of the shape memory polymer matrix drops below the glass transition temperature, and the stiffness of the electrochromic stiffness core layer recovers.

[0007] As a further implementation, the conductive network is a carbon fiber felt conductive network; the inner skin is bonded with reinforcing ribs, and adjacent reinforcing ribs maintain a set spacing; the electro-variable stiffness core layer is divided into multiple independent heating zones along the longitudinal direction of the front of the vehicle, and the conductive network of each independent heating zone is independently connected to an external power supply circuit, automatically cutting off power when the set temperature is exceeded; a glass cloth isolation layer is provided between the outer skin and the electro-variable stiffness core layer, and between the electro-variable stiffness core layer and the inner skin.

[0008] Secondly, the present invention also provides a variable stiffness control system for a rail transit vehicle head shell, comprising: a vehicle speed sensor for acquiring real-time vehicle speed signals; a strain sensor embedded in the inner side of the outer skin of the head shell; and a temperature sensor embedded in the electro-variable stiffness core layer of the head shell. The vehicle speed sensor, the strain sensor, and the temperature sensor are all connected to a controller. The controller stores a mapping relationship between vehicle speed and target stiffness. The controller queries the mapping relationship based on the real-time vehicle speed signal to obtain the target stiffness and performs closed-loop adjustment based on the strain signal and the temperature signal. The controller is connected to a zoned power supply unit, which independently supplies power to each independent heating zone of the electro-variable stiffness core layer.

[0009] As a further implementation, the strain sensor is a fiber Bragg grating sensor, and the temperature sensor is a negative temperature coefficient thermistor or a fiber Bragg grating sensor; the controller adopts a dual-channel redundant structure, with the backup control channel taking over control when the main control channel fails; when the vehicle is powered off, the partition power supply unit stops supplying power, and the electro-variable stiffness core layer automatically returns to a high stiffness state; the controller adjusts the power supply through pulse width modulation, and forces a power cut-off when the temperature exceeds the over-temperature protection threshold; the power supply of each independent heating zone is independently controlled by the controller, and if any independent heating zone fails, that heating zone automatically shuts off power, while the other heating zones are unaffected.

[0010] Thirdly, the present invention also provides a method for controlling the variable stiffness of the front shell of a rail transit vehicle, comprising the following steps: After the system is powered on and initialized, the real-time vehicle speed signal of the rail vehicle is collected by the vehicle speed sensor, the skin surface strain signal is collected by the strain sensor, and the core layer real-time temperature signal is collected by the temperature sensor. Kalman filtering and data fusion processing are performed on the data from the vehicle speed sensor, strain sensor, and temperature sensor to obtain the fused real-time vehicle speed, actual stiffness state, and core layer temperature. The controller queries the pre-stored mapping relationship between vehicle speed and target stiffness based on the fused real-time vehicle speed, and calculates the target stiffness; based on the target stiffness and the current core temperature, it calculates the required driving voltage through a voltage calculation function and limits the driving voltage within a safe range. When the real-time vehicle speed is lower than or equal to the low-speed threshold, the conductive network of the electrochromic stiffness core layer is energized, and the core layer temperature is raised above the glass transition temperature through Joule heating, and the core layer enters the low-stiffness rubber state; when the real-time vehicle speed is higher than or equal to the high-speed threshold, the power supply to the conductive network is uniformly disconnected, and the core layer recovers to the high-stiffness glass state through natural cooling; when the real-time vehicle speed is between the low-speed threshold and the high-speed threshold, the independent heating zones are adjusted by pulse width modulation, so that the core layer stiffness transitions linearly between low stiffness and high stiffness. The controller uses the target stiffness as the set value and the actual stiffness state fed back by the strain sensor as the feedback value. It adopts a proportional-integral-derivative control algorithm to perform closed-loop regulation of the power supply to each heating zone, so that the actual stiffness tracks the target stiffness. When the real-time temperature of the core layer reaches or exceeds the safety limit, the power supply to the conductive network is forcibly disconnected. When the vehicle loses power or the control system malfunctions, the zone power supply unit automatically stops supplying power to the conductive network, the electro-variable stiffness core layer automatically recovers to a high-stiffness glass state through natural cooling, and the front body shell enters a fail-safe mode.

[0011] As a further implementation method, the low-speed threshold of the vehicle speed is 80km / h, and the high-speed threshold is 160km / h; the switching time from the low-stiffness rubber state to the high-stiffness glass state does not exceed 5 seconds, and the switching time from the high-stiffness glass state to the low-stiffness rubber state does not exceed 30 seconds. The safe upper limit temperature is 85°C.

[0012] Fourthly, the present invention also provides a method for manufacturing a rail transit vehicle head shell, comprising the following steps: Apply a release agent and gel coat to the inner surface of the single-sided female mold; An outer skin dry fiber fabric is sequentially laid inside the single-sided negative mold; After the pre-cured electro-variable stiffness film is cut according to the curved surface of the car front, it is laid on the inner side of the dry fiber fabric of the outer skin. The electro-variable stiffness film has an embedded conductive network and leads out electrodes. The upper and lower surfaces of the electro-variable stiffness film are pre-bonded with a glass cloth isolation layer with a thickness of 0.1mm. An inner skin dry fiber fabric is laid on the inner side of the electro-variable stiffness film, and reinforcing rib prepreg is laid according to the position of the reinforcing rib. The reinforcing rib prepreg is a T-shaped or cap-shaped glass fiber reinforced polymer or carbon fiber reinforced polymer reinforcing rib, and the spacing between adjacent reinforcing ribs is 200-400mm. Lay out the release liner and flow guide net in sequence; Cover and seal the mold edges with an airtight bag film, and connect the vacuum pump to the resin injection port; Start the vacuum pump to evacuate to -0.095 to -0.1 MPa, maintain the pressure and check for leaks for no less than 30 minutes, and ensure that the pressure drop does not exceed 5% to confirm that the airtightness is qualified. Resin is injected into the mold under negative pressure, so that the resin wets the outer skin dry fiber fabric, the surface of the electro-variable stiffness film and the inner skin dry fiber fabric, thereby realizing micro-mechanical interlocking between the skin and the core material interface. Maintain vacuum, and cure by stepwise heating within the range of 80-120℃, holding for 2-4 hours. The volume fraction of the fiber in the cured shell should not be less than 55%, and the porosity should not exceed 3%. Release the vacuum, remove the airtight bag membrane, demold and take out the shell, and perform edge trimming, drilling and installation of embedded parts; The electrodes led out from the electrovariable stiffness film are passed through the skin via a sealing connector and connected to the vehicle controller; the strain sensor is embedded in the key measuring point on the inner side of the outer skin, and the temperature sensor is embedded inside the electrovariable stiffness film, with synchronous wiring and fixation.

[0013] As a further implementation, the shape memory polymer matrix of the electrovariable stiffness film is embedded with a continuous carbon fiber felt conductive network, the carbon fiber felt has a mass fraction of 3% to 8%, a glass transition temperature of 55 to 75°C, and a driving voltage of 24 to 60V DC; in step nine, the volume fraction of the shell fiber obtained after curing is not less than 55%, and the porosity does not exceed 3%.

[0014] As a further implementation, the strain sensor is a fiber Bragg grating sensor, embedded inside the outer skin; and the inner surface of the single-sided female mold is coated with a gel coat layer after the release agent is applied.

[0015] As a further implementation, resin permeates the micropores on the surface of the electro-variable stiffness film to achieve interfacial micromechanical interlocking between the outer skin, the electro-variable stiffness core layer, and the inner skin.

[0016] Compared with the prior art, the advantages and positive effects of this invention are: This invention uses an electro-induced shape memory polymer film as the core layer of a sandwich structure and utilizes an embedded carbon fiber felt conductive network to generate Joule heat to drive the shape memory polymer matrix past its glass transition temperature. This enables rapid online adjustment of the stiffness of the vehicle front shell structure. The switching time from high stiffness to low stiffness is no more than 30 seconds, and the switching time from low stiffness to high stiffness is no more than 5 seconds. This overcomes the fundamental defect of existing fixed stiffness vehicle front shells that cannot simultaneously meet the dual requirements of low-speed vibration absorption and high-speed stable load bearing.

[0017] This invention establishes a mapping relationship between vehicle speed and target stiffness, and combines Kalman filter multi-source data fusion, voltage calculation function safety limiting, fiber Bragg grating strain sensor and temperature sensor dual feedback closed loop, and proportional-integral-derivative control algorithm to achieve real-time and accurate tracking of stiffness state. At low speeds, the core layer is in a low-stiffness rubber state, improving vibration absorption capacity by 30% to 40%. At high speeds, the core layer automatically recovers to a high-stiffness glass state, ensuring aerodynamic stability and effectively balancing low-speed ride comfort with high-speed structural safety.

[0018] This invention divides the electrovariable stiffness core layer into 4 to 6 independent heating zones along the longitudinal direction of the vehicle head, with independent power supply and control for each zone. The proportional-integral-derivative parameters of each zone are independently set, and the failure of any zone does not affect the normal operation of the other zones. When the vehicle loses power, the core layer automatically restores to a high stiffness state, which has failure safety characteristics. The controller adopts a dual-channel redundant structure, and the backup control channel takes over the control when the main control channel fails. The system reliability meets the high reliability requirements of rail transit.

[0019] This invention employs a single-sided negative mold vacuum infusion integrated process to simultaneously impregnate and cure the outer skin, electro-variable stiffness film, inner skin, and reinforcing ribs in a single process, thereby achieving micro-mechanical interlocking at the interface between the skin and the core material. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the front shell structure of the present invention. Figure 2 This is a schematic diagram of the electro-induced shape memory polymer in the power-off state of the present invention. Figure 3 This is a schematic diagram of the electro-induced shape memory polymer of the present invention under energized heating. Figure 4 The system control logic diagram of the present invention Figure 5 This is a graph showing the vehicle speed-stiffness-voltage mapping relationship of the present invention. Figure 6 This is a schematic diagram of the manufacturing method of the present invention. Figure 7 This is a schematic diagram of the power supply layout for the front of the vehicle according to the present invention. Figure 8 This is a graph showing the relationship between the vibration acceleration of the vehicle's front end and the vehicle speed according to the present invention. Figure 9 This is a graph showing the relationship between the energy storage modulus of the vehicle front and temperature in this invention. In the diagram: 1. Outer skin; 2. Electro-variable stiffness core layer; 3. Inner skin; 4. Reinforcing rib; 5. Isolation layer; 6. Vehicle speed sensor; 7. Strain sensor; 8. Temperature sensor. Detailed Implementation

[0022] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is intended to include the plural form as well. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] This invention relates to a front-end housing for rail transit vehicles, a control system, a control method, and a manufacturing method. The front-end housing uses an electro-induced shape memory polymer film as the middle core layer of a sandwich structure. Joule heating is generated by energizing an embedded carbon fiber felt conductive network, driving the shape memory polymer matrix across the glass transition temperature. This allows for rapid and reversible switching between a high-stiffness glassy state and a low-stiffness rubbery state, simultaneously meeting the vibration absorption requirements of rail vehicles during low-speed operation and the stable load-bearing requirements during high-speed operation.

[0025] Example 1 This embodiment provides a rail transit vehicle headstock housing, such as Figure 1As shown, the front shell of the rail transit vehicle adopts a three-layer sandwich structure, consisting of an outer skin 1, an electrovariable stiffness core layer 2, and an inner skin 3, from the outside in. The outer skin 1 is made of carbon fiber reinforced resin composite material and is located on the outermost side of the shell, directly bearing the aerodynamic external load and providing the outer surface of the front. The outer skin 1 is laid in a center-symmetrical manner, in the order of 0°→45°→-45°→90°, and then repeated symmetrically in the reverse order, with a thickness of 1.5~3.0mm. The electrovariable stiffness core layer 2 is stacked on the inner side of the outer skin 1 and consists of a shape memory polymer matrix and a conductive network embedded in the shape memory polymer matrix. The conductive network is connected to the external power supply circuit; the thickness of the electrovariable stiffness core layer 2 is 2~8mm. The inner skin 3 is stacked inside the electrovariable stiffness core layer 2 and is made of fiber-reinforced resin composite material. It supports the vehicle's equipment and provides a mounting surface for the interior trim. The thickness of the inner skin 3 is 1.2–2.5 mm, and reinforcing ribs 4 are bonded to its inner side. The spacing between adjacent reinforcing ribs 4 is 200–400 mm. The working principle of the above three-layer structure is analogous to that of an I-beam: the outer skin 1 and inner skin 3 are analogous to flanges, bearing tensile and compressive loads respectively; the electrovariable stiffness core layer 2 is analogous to a web, bearing shear and achieving online stiffness adjustment.

[0026] like Figure 2 and Figure 3 As shown, the variable stiffness mechanism of the electro-variable stiffness core layer 2 can be divided into the following two states. When the conductive network is energized, the current flows through the carbon fiber felt conductive network, generating heat according to the Joule heating principle (Q=I²Rt), causing the temperature of the shape memory polymer matrix to rise from room temperature to above the glass transition temperature (55-75℃) within 2-5 seconds. At this time, the molecular chain segments of the shape memory polymer matrix are activated and curled, and the material changes from a glassy state to a rubbery state. The energy storage modulus of the electro-variable stiffness core layer 2 is significantly reduced from 1-3 GPa to 10-100 MPa, and the overall front shell enters a low-stiffness vibration absorption mode, which is beneficial for absorbing line vibration excitation under low-speed operating conditions and improving ride comfort. When the conductive network is de-energized, the shape memory polymer matrix dissipates heat through natural convection and radiation, gradually lowering its temperature below the glass transition temperature. At this point, the molecular chain segments refreeze, the material returns to a glassy state, and the energy storage modulus of the electrovariable stiffness core layer 2 recovers to a high stiffness level of 1–3 GPa. The overall vehicle front shell enters a high-stiffness stable load-bearing mode, ensuring aerodynamic stability and structural safety during high-speed operation. With a shape fixation rate greater than 96% and a shape recovery rate greater than 93%, the electrovariable stiffness core layer 2 maintains a consistent stiffness state after multiple cyclic switching cycles, ensuring long-term reliability.

[0027] The conductive network is a carbon fiber felt conductive network with a carbon fiber felt mass fraction of 3% to 8% and an electrical conductivity of 0.5 to 5 S / m; the driving voltage of the conductive network is 24 to 60 V DC. An isolation layer 5 is provided between the outer skin 1 and the electrovariable stiffness core layer 2, and between the electrovariable stiffness core layer 2 and the inner skin 3. The isolation layer 5 is a 0.1 mm thick glass cloth, which isolates the carbon fiber felt conductive network from the carbon fiber structure in the outer skin 1 and the inner skin 3, preventing electrochemical corrosion caused by potential differences between different carbon fiber materials, thereby ensuring the structural reliability of the shell for long-term use.

[0028] The electro-variable stiffness core layer 2 is divided into several independent heating zones along the longitudinal direction of the vehicle front. The conductive network of each independent heating zone is independently connected to an external power supply circuit. Each independent heating zone is equipped with an independent over-temperature protection element, which automatically cuts off power when the temperature exceeds 85℃. For example... Figure 7 As shown, the front housing is longitudinally divided into four independent heating zones: the nose tip heating zone, the left side wall heating zone, the right side wall heating zone, and the underframe heating zone. Each zone is connected to the zone power supply unit via independent electrode leads. When any independent heating zone fails, the over-temperature protection element of that zone automatically cuts off the power, while the other heating zones remain unaffected and continue to operate normally, thus achieving fault isolation and meeting the structural reliability requirements of rail transit.

[0029] Example 2 This embodiment provides a variable stiffness control system for a rail transit vehicle head shell, including a speed sensor 6, a strain sensor 7, a temperature sensor 8, a controller, and a zoned power supply unit; the speed sensor 6, strain sensor 7, and temperature sensor 8 form a multi-source sensor. The speed sensor 6 is installed on the rail vehicle's onboard network or axle end to collect the real-time speed signal of the rail vehicle and transmit the signal to the controller. The strain sensor 7 is embedded inside the outer skin 1 of the head shell to collect the strain signal on the skin surface and transmit the strain signal to the controller to reflect the actual stiffness state of the electro-variable stiffness core layer 2. The temperature sensor 8 is embedded inside the electro-variable stiffness core layer 2 of the head shell to collect the real-time temperature signal of the core layer and transmit the temperature signal to the controller to monitor the temperature state of the shape memory polymer matrix. The controller is connected to the vehicle speed sensor 6, strain sensor 7, and temperature sensor 8. The controller stores a mapping relationship between vehicle speed and target stiffness. It queries this mapping relationship based on the real-time vehicle speed signal to obtain the target stiffness and performs closed-loop adjustment of the power supply duty cycle based on the strain and temperature signals, outputting control commands to the zoned power supply unit. The zoned power supply unit is connected to the controller and, according to the controller's commands, independently supplies power to each independent heating zone of the electrochromic stiffness core layer 2, driving the conductive network to generate Joule heating and achieving independent adjustment of the stiffness of each zone.

[0030] In this embodiment, the control system forms a "perception-decision-execution" closed loop: the vehicle speed sensor 6 provides feedforward, and the controller determines the target stiffness based on the mapping relationship between vehicle speed and target stiffness; the strain sensor 7 provides real-time feedback of the skin surface strain to assess the actual stiffness state; the temperature sensor 8 monitors the core temperature in real time to prevent overshoot and overheating; the three types of sensor signals jointly drive the controller to perform closed-loop adjustment of the power supply duty cycle to achieve accurate tracking of the stiffness state.

[0031] The strain sensor 7 is a fiber Bragg grating sensor, embedded in key measuring points such as the nose cone, driver's cab roof, and side window upper beam on the inner side of the outer skin 1. The temperature sensor 8 is a negative temperature coefficient thermistor or fiber Bragg grating sensor, embedded inside the electrovariable stiffness core layer 2. The fiber Bragg grating sensor can simultaneously measure strain and temperature, achieving dual-parameter sensing, and its embedded installation method does not affect the overall structural performance of the shell. The resistance value of the negative temperature coefficient thermistor decreases as the temperature increases, and the controller can calculate the real-time temperature of the core layer by collecting its resistance value.

[0032] The controller employs a dual-channel redundant structure, including a main control channel and a backup control channel. Under normal operating conditions, the main control channel receives three types of sensor signals, performs vehicle speed-target stiffness mapping queries, runs closed-loop control algorithms, and outputs power supply commands. If the main control channel fails, the backup control channel automatically takes over control within 200ms, ensuring continuous operation of the control system. When the vehicle is powered off, the zoned power supply unit stops supplying power to the electrochromic stiffness core layer 2. The conductive network no longer generates Joule heating, and the shape memory polymer matrix temperature naturally drops below the glass transition temperature. The electrochromic stiffness core layer 2 automatically returns to a high-stiffness state, and the front body enters a fail-safe mode. The controller adjusts the power supply through pulse width modulation. When the core layer temperature collected by temperature sensor 8 exceeds the over-temperature protection threshold, the controller forcibly disconnects the power supply to the conductive network to prevent the shape memory polymer matrix from overheating and failing. The controller calculates and independently adjusts the power supply duty cycle for each independent heating zone. If any independent heating zone fails, that zone is automatically powered off, while the other heating zones remain unaffected.

[0033] Example 3 This embodiment provides a method for controlling the variable stiffness of the front shell of a rail transit vehicle. The control method is executed by the aforementioned control system and includes the following steps: Figure 4 As shown.

[0034] After system power-on initialization, the real-time vehicle speed signal is acquired through vehicle speed sensor 6, the surface strain signal of the skin is acquired through strain sensor 7 embedded inside the outer skin 1, and the real-time temperature signal of the core layer is acquired through temperature sensor 8 embedded inside the electrovariable stiffness core layer 2. Kalman filtering and data fusion processing are performed on the above multi-source sensor data to filter out sensor noise, obtaining the fused real-time vehicle speed, actual stiffness state, and core layer temperature. Kalman filtering can effectively suppress sensor measurement noise, improve the accuracy of stiffness state estimation, and provide reliable input for subsequent control decisions.

[0035] The controller queries the pre-stored mapping relationship between vehicle speed and target stiffness based on the fused real-time vehicle speed, and calculates the target stiffness. For example... Figure 5 As shown, this mapping relationship takes real-time vehicle speed as input and target stiffness as output: at low speeds (≤80km / h), the target stiffness is rubber-like low stiffness (approximately 50MPa); at high speeds (≥160km / h), the target stiffness is glass-like high stiffness (approximately 2000MPa); and the target stiffness in the intermediate speed range is linearly interpolated. Based on the target stiffness K and the current core temperature T, the required driving voltage is calculated using the voltage calculation function V=g(K,T), and the calculation results are subjected to safety limiting processing to restrict the driving voltage within the range of 24~60V DC to prevent overvoltage damage to the conductive network.

[0036] Based on the comparison between the real-time vehicle speed and a preset threshold, the controller outputs power supply commands to the partition power supply unit in three different scenarios. When the real-time vehicle speed is lower than or equal to the low-speed threshold (80 km / h), the controller determines that the vehicle is in a low-speed vibration-absorbing condition and instructs the partition power supply unit to energize the conductive network of the electrochromic stiffness core layer 2. The conductive network generates Joule heating, raising the temperature of the shape memory polymer matrix above its glass transition temperature. The electrochromic stiffness core layer 2 enters a low-stiffness rubber state, and the front body is in vibration-absorbing mode. The switching time does not exceed 30 seconds. When the real-time vehicle speed is higher than or equal to the high-speed threshold (160 km / h), the controller determines that the vehicle is in a high-speed load-bearing condition and instructs the partition power supply unit to disconnect the power supply to the conductive network. The shape memory polymer matrix cools down to below its glass transition temperature through natural heat dissipation, and the electrochromic stiffness core layer 2 returns to a high-stiffness glass state. The front body is in a stable load-bearing mode. The switching time does not exceed 5 seconds. When the real-time vehicle speed is between 80km / h and 160km / h, the controller adjusts the power supply duty cycle through pulse width modulation, so that the average heating power of the conductive network changes linearly between the maximum value and zero, thereby making the stiffness of the electrovariable stiffness core layer 2 transition linearly between low stiffness and high stiffness, avoiding abrupt changes in stiffness state.

[0037] The controller sets the proportional-integral-derivative control parameters for each independent heating zone of the electro-variable stiffness core layer 2, including the nose tip heating zone, the left side wall heating zone, the right side wall heating zone, and the base frame heating zone. The power supply duty cycle of each zone is adjusted independently, and the drive signal is independently output to the conductive network of each zone through pulse width modulation. When any independent heating zone fails, the zone is automatically powered off, while the other heating zones are unaffected, thus achieving fault isolation.

[0038] The controller uses the target stiffness as the setpoint and the actual stiffness state fed back by strain sensor 7 as the feedback value. It employs a proportional-integral-derivative (PI-DE) control algorithm to perform closed-loop adjustment of the power supply duty cycle, ensuring that the actual stiffness of the electrovariable stiffness core layer 2 tracks the target stiffness. The PI-DE control algorithm uses the difference between the target stiffness and the actual stiffness as the error input. Through comprehensive calculations of the proportional, integral, and derivative components, it outputs a corrected power supply duty cycle command, driving the zoned power supply unit to adjust the power supply to each independent heating zone, eliminating steady-state errors and suppressing dynamic overshoot. When the real-time core layer temperature collected by temperature sensor 8 reaches or exceeds the safe upper limit (85℃), the controller forcibly disconnects the power supply to the conductive network to prevent damage to the shape memory polymer matrix due to overheating.

[0039] When the vehicle loses power or the control system malfunctions, the zone power supply unit automatically stops supplying power to the conductive network. The electro-variable stiffness core layer 2 automatically recovers to a high-stiffness glass state through natural cooling, and the front shell enters a fail-safe mode to ensure structural safety under emergency conditions.

[0040] Example 4 This embodiment provides a method for manufacturing a rail transit vehicle head shell, employing a single-sided female mold vacuum introduction integrated molding process, specifically including the following steps, such as... Figure 6 As shown.

[0041] Apply a release agent to the inner surface of the single-sided female mold, and then apply a gel coat layer; the gel coat layer can improve the weather resistance and appearance quality of the outer surface of the shell.

[0042] The outer skin dry fiber fabric is laid sequentially in the single-sided negative mold. The laying sequence is symmetrical in the middle, in the order of 0°→45°→-45°→90°, and then repeated symmetrically in the opposite order. Pay attention to fiber orientation and overlap to ensure the multi-directional load-bearing capacity of the outer skin 1.

[0043] The pre-cured electrostrictive stiffness film is cut according to the curved surface of the vehicle front and then laminated onto the inner side of the dry fiber fabric of the outer skin. This electrostrictive stiffness film contains an embedded conductive network and leads out electrodes. An insulating layer 5 (0.1 mm thick glass cloth) is pre-adhered to the upper and lower surfaces of the electrostrictive stiffness film to prevent electrochemical corrosion. The electrostrictive stiffness film has a shape memory polymer matrix with an embedded continuous carbon fiber felt conductive network. The carbon fiber felt has a mass fraction of 3%–8%, a glass transition temperature of 55–75°C, and a driving voltage of 24–60 V DC.

[0044] An inner skin dry fiber fabric is laid inside the electrovariable stiffness film, and reinforcing rib prepreg is laid according to the position of the reinforcing ribs; the reinforcing rib prepreg is a T-shaped or cap-shaped glass fiber reinforced polymer or carbon fiber reinforced polymer reinforcing rib, and the spacing between adjacent reinforcing ribs is 200-400mm. The reinforcing ribs 4 are bonded to the inner skin 3 to improve the local stiffness of the inner skin 3, prevent buckling under concentrated loads, and transfer the concentrated loads to the overall shell structure.

[0045] The release cloth and the flow guide net are laid in sequence; the flow guide net forms a resin flow channel, ensuring that the resin can evenly wet all the dry fiber fabric under negative pressure.

[0046] Cover and seal the mold edges with an airtight bag film, and connect the vacuum pump to the resin injection port to ensure a reliable seal.

[0047] Start the vacuum pump to evacuate the inside of the mold to -0.095 to -0.1 MPa, maintain the pressure and check for leaks for no less than 30 minutes, and ensure that the pressure drop does not exceed 5%. Resin injection can only proceed after confirming that the airtightness is qualified.

[0048] Resin is injected into the mold under negative pressure. The resin wets the outer skin dry fiber fabric, the surface of the electro-variable stiffness film and the inner skin dry fiber fabric along the guide net. At the same time, it penetrates the micropores on the surface of the electro-variable stiffness film to achieve micro-mechanical interlocking of the interface between the outer skin 1, the electro-variable stiffness core layer 2 and the inner skin 3.

[0049] Maintain a vacuum and cure the resin by stepwise heating within the range of 80–120°C, holding for 2–4 hours to ensure complete curing. The resulting shell should have a fiber volume fraction of not less than 55% and a porosity of not more than 3%, ensuring excellent mechanical properties.

[0050] After curing, the vacuum is released, the airtight bag film is removed, the shell is demolded and removed, the edges are trimmed and drilled, and the embedded parts are installed.

[0051] Electrodes from the electrochromic stiffness film are protruded through the skin via sealed connectors and connected to the vehicle controller. Fiber Bragg grating strain sensors are embedded at key measuring points such as the inner nose cone of the outer skin 1, the driver's cab roof, and the upper beam of the side windows. Temperature sensor 8 is embedded inside the electrochromic stiffness film and simultaneously wired and fixed. The vehicle controller adopts a dual-channel redundant structure. In the event of a failure in the main control channel, the backup control channel takes over control within 200ms. When the vehicle loses power, the conductive network stops supplying power, the electrochromic stiffness film automatically returns to a high-stiffness state, and the front body enters a fail-safe mode.

[0052] like Figure 8 and Figure 9 As shown, when the front end shell of this invention is in a low-speed operating condition, the electro-variable stiffness core layer 2 is in a low-stiffness rubber state, and its loss modulus peaks near the glass transition temperature, significantly enhancing its ability to dissipate vibration energy. The vibration acceleration is significantly reduced compared to a traditional fixed-stiffness front end shell, and the vibration absorption capacity is increased by 30%–40%. In a high-speed operating condition, the electro-variable stiffness core layer 2 reverts to a high-stiffness glass state, and the energy storage modulus returns to the glass state level. The overall stiffness of the front end shell is comparable to that of a traditional fixed-stiffness front end shell, ensuring aerodynamic stability. Because the shape fixation rate is higher than 96% and the shape recovery rate is higher than 93%, the electro-variable stiffness core layer 2 can maintain a consistent stiffness state after multiple cycles, ensuring long-term reliability.

[0053] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A rail transit vehicle head shell, characterized in that, include: An outer skin is made of carbon fiber reinforced resin composite material; an electrostrictive stiffness core layer is provided on the inner side of the outer skin, the electrostrictive stiffness core layer is composed of a shape memory polymer matrix and a conductive network embedded in the shape memory polymer matrix, the conductive network being connected to an external power supply circuit; an inner skin is stacked on the inner side of the electrostrictive stiffness core layer, the inner skin being made of fiber reinforced resin composite material. The outer skin, the electrochromic stiffness core layer, and the inner skin form a three-layer sandwich structure. When the conductive network is energized, it generates Joule heating, which raises the temperature of the shape memory polymer matrix above the glass transition temperature, and the stiffness of the electrochromic stiffness core layer decreases. When the power is turned off, the temperature of the shape memory polymer matrix drops below the glass transition temperature, and the stiffness of the electrochromic stiffness core layer recovers.

2. The rail transit vehicle head shell according to claim 1, characterized in that, The conductive network is a carbon fiber felt conductive network; the inner skin has reinforcing ribs bonded to its inner side, and adjacent reinforcing ribs maintain a set spacing; the electro-variable stiffness core layer is divided into multiple independent heating zones along the longitudinal direction of the front of the vehicle, and the conductive network of each independent heating zone is independently connected to an external power supply circuit, automatically cutting off power when the set temperature is exceeded; a glass cloth isolation layer is provided between the outer skin and the electro-variable stiffness core layer, and between the electro-variable stiffness core layer and the inner skin.

3. A variable stiffness control system for the head shell of a rail transit vehicle, characterized in that, include: The system includes a speed sensor for acquiring real-time vehicle speed signals, a strain sensor embedded inside the outer skin of the front housing, and a temperature sensor embedded inside the electrostrictive stiffness core layer of the front housing. All three sensors are connected to a controller, which stores a mapping relationship between vehicle speed and target stiffness. The controller obtains the target stiffness by querying the mapping relationship based on the real-time vehicle speed signal and performs closed-loop adjustment based on the strain and temperature signals. The controller is connected to a zoned power supply unit, which independently supplies power to each independent heating zone of the electrostrictive stiffness core layer.

4. The variable stiffness control system according to claim 3, characterized in that, The strain sensor is a fiber Bragg grating sensor, and the temperature sensor is a negative temperature coefficient thermistor or a fiber Bragg grating sensor. The controller adopts a dual-channel redundant structure, with the backup control channel taking over control when the main control channel fails. When the vehicle is powered off, the partition power supply unit stops supplying power, and the electro-variable stiffness core layer automatically returns to a high stiffness state. The controller adjusts the power supply through pulse width modulation, and forces a power cut-off when the temperature exceeds the over-temperature protection threshold. The power supply of each independent heating zone is independently controlled by the controller. When any independent heating zone fails, that heating zone automatically shuts off power, while the other heating zones remain unaffected.

5. A method for controlling the variable stiffness of a rail transit vehicle head shell, characterized in that, Includes the following steps: After the system is powered on and initialized, the real-time vehicle speed signal of the rail vehicle is collected by the vehicle speed sensor, the skin surface strain signal is collected by the strain sensor, and the core layer real-time temperature signal is collected by the temperature sensor. Kalman filtering and data fusion processing are performed on the data from the vehicle speed sensor, strain sensor, and temperature sensor to obtain the fused real-time vehicle speed, actual stiffness state, and core layer temperature. The controller queries the pre-stored mapping relationship between vehicle speed and target stiffness based on the fused real-time vehicle speed, and calculates the target stiffness. Based on the target stiffness and the current core temperature, the required driving voltage is calculated using a voltage calculation function, and the driving voltage is limited within a safe range. When the real-time vehicle speed is lower than or equal to the low-speed threshold, the conductive network of the electrochromic stiffness core layer is energized, and the core layer temperature is raised above the glass transition temperature through Joule heating, and the core layer enters the low-stiffness rubber state; when the real-time vehicle speed is higher than or equal to the high-speed threshold, the power supply to the conductive network is uniformly disconnected, and the core layer recovers to the high-stiffness glass state through natural cooling; when the real-time vehicle speed is between the low-speed threshold and the high-speed threshold, the independent heating zones are adjusted by pulse width modulation, so that the core layer stiffness transitions linearly between low stiffness and high stiffness. The controller uses the target stiffness as the set value and the actual stiffness state fed back by the strain sensor as the feedback value. It adopts a proportional-integral-derivative control algorithm to perform closed-loop regulation of the power supply to each heating zone, so that the actual stiffness tracks the target stiffness. When the real-time temperature of the core layer reaches or exceeds the safety limit, the power supply to the conductive network is forcibly disconnected. When the vehicle loses power or the control system malfunctions, the zone power supply unit automatically stops supplying power to the conductive network, the electro-variable stiffness core layer automatically recovers to a high-stiffness glass state through natural cooling, and the front body shell enters a fail-safe mode.

6. The variable stiffness control method according to claim 5, characterized in that, The low-speed threshold for vehicle speed is 80 km / h, and the high-speed threshold is 160 km / h; the switching time from low-stiffness rubber state to high-stiffness glass state does not exceed 5 seconds, and the switching time from high-stiffness glass state to low-stiffness rubber state does not exceed 30 seconds. The safe upper limit temperature is 85°C.

7. A method for manufacturing a front shell of a rail transit vehicle, characterized in that, Includes the following steps: Apply a release agent and gel coat to the inner surface of the single-sided female mold; An outer skin dry fiber fabric is sequentially laid inside the single-sided negative mold; After the pre-cured electro-variable stiffness film is cut according to the curved surface of the car front, it is laid on the inner side of the dry fiber fabric of the outer skin. The electro-variable stiffness film has an embedded conductive network and leads out electrodes. The upper and lower surfaces of the electro-variable stiffness film are pre-bonded with glass cloth isolation layers. An inner skin dry fiber fabric is laid on the inner side of the electrochromic stiffness film, and reinforcing rib prepreg is laid according to the position of the reinforcing rib, with a set spacing between adjacent reinforcing ribs. Lay out the release fabric and the flow guide net in sequence; Cover and seal the mold edges with an airtight bag film, and connect the vacuum pump to the resin injection port; Start the vacuum pump to create a vacuum and confirm that the airtightness is acceptable; Resin is injected into the mold under negative pressure, so that the resin wets the outer skin dry fiber fabric, the surface of the electro-variable stiffness film and the inner skin dry fiber fabric, thereby realizing micro-mechanical interlocking between the skin and the core material interface. Maintain vacuum, and cure by stepwise temperature increase within the range of 80-120℃, holding for 2-4 hours; Release the vacuum, remove the airtight bag membrane, demold and take out the shell, and perform edge trimming, drilling and installation of embedded parts; The electrodes led out from the electrovariable stiffness film are passed through the skin via a sealing connector and connected to the vehicle controller; the strain sensor is embedded in the key measuring point on the inner side of the outer skin, and the temperature sensor is embedded inside the electrovariable stiffness film, with synchronous wiring and fixation.

8. The manufacturing method according to claim 7, characterized in that, The electrovariable stiffness film has a shape memory polymer matrix with an embedded continuous carbon fiber felt conductive network, the carbon fiber felt having a mass fraction of 3% to 8%, a glass transition temperature of 55 to 75°C, and a driving voltage of 24 to 60V DC.

9. The manufacturing method according to claim 7, characterized in that, The strain sensor is a fiber Bragg grating sensor, which is embedded on the inner side of the outer skin; the inner surface of the single-sided female mold is coated with a gel coat layer after the release agent is applied.

10. The manufacturing method according to claim 7, characterized in that, The resin permeates the micropores on the surface of the electro-variable stiffness film, achieving micromechanical interlocking at the interface between the outer skin, the electro-variable stiffness core layer, and the inner skin.

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