Hydraulically-driven anti-freezing automobile active diffuser and control method thereof

Abstract

The invention discloses a hydraulically-driven anti-freezing automobile active diffuser and a control method thereof in the technical field of automobile manufacturing, and the hydraulically-driven anti-freezing automobile active diffuser comprises a control output mechanism which is installed on the upper portion of an anti-collision beam and comprises a controller and a hydraulic pump, and the controller controls power output of the hydraulic pump according to a whole automobile instruction; the output end of the hydraulic pump pushes pressurized liquid to the hydraulic rod through the hydraulic guide pipe; the mounting base is mounted at the lower part of the anti-collision beam, and the lower end is rotationally connected with the diffuser panel; the two ends of the hydraulic rod are rotationally connected with the mounting base and the diffuser panel correspondingly, and the rotating angle of the diffuser panel is controlled through stretching and retracting; and the heating device is mounted on the surface of the diffuser panel and used for heating the whole structure based on the controller. The heating anti-freezing function is achieved through the heating device, if a local freezing state is generated in frost weather, the basic function can be achieved through heating, in addition, the hydraulic rod can output high transmission force, and icebreaking starting is easier under the freezing condition.

Description

Technical Field

[0001] This invention relates to a hydraulically driven antifreeze active diffuser for automobiles and its control method, belonging to the field of automobile manufacturing technology. Background Art

[0002] To optimize vehicle aerodynamic efficiency, improvements to the body structure design are commonly used to enhance energy efficiency, reduce carbon emissions, and improve driving performance. Typical measures include drag control. In electrified vehicles, streamlined optimization has a significant positive effect on increasing driving range. The air deflector (commonly known as the diffuser) located in the rear chassis is a key area for optimization, as it enhances vehicle handling stability by suppressing lift generation. It is worth noting that the optimal geometry of the diffuser in off-road conditions conflicts with the chassis structure design, and an overemphasis on aerodynamic performance in the diffuser's shape may negatively impact the overall aesthetics of the vehicle.

[0003] Existing automotive active diffusers are prone to icing and frost formation on their blades during winter rain and snow, especially in cold and damp conditions, which can cause the diffuser blades to fail to open. Therefore, it is even more important to consider how to quickly restore the diffuser's function in freezing weather. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hydraulically driven antifreeze automotive active diffuser and its control method. The heating and antifreeze function is achieved through a heating device. In frost weather, if a local freezing state occurs, the basic function can be achieved through heating.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a hydraulically driven antifreeze automotive active diffuser, comprising: Control output mechanism: Installed on the upper part of the anti-collision beam, including a controller and a hydraulic pump. The controller controls the power output of the hydraulic pump according to the vehicle command. The output end of the hydraulic pump pushes pressurized liquid to the hydraulic rod through a hydraulic conduit. Mounting base: Installed on the lower part of the anti-collision beam, with its lower end rotatably connected to the diffuser panel; Hydraulic rod: Both ends are rotatably connected to the mounting base and the diffuser panel respectively, and the rotation angle of the diffuser panel is controlled by extension and retraction; Heating device: Installed on the surface of the diffuser panel, it heats the entire structure based on the controller.

[0006] Furthermore, the controller dynamically calculates the icing probability based on environmental parameters, and then determines the preheating program based on the icing probability, only in response to the icing probability exceeding a preset threshold.

[0007] Furthermore, the formula for calculating the icing probability is as follows:

[0008] In the formula, P f δ represents the probability of icing; T represents the ambient temperature; RH represents the relative humidity of the air; T0 represents the reference freezing point; α, β, and γ represent the material characteristic coefficients; δ t Weighted by the duration of sustained low temperature.

[0009] Furthermore, the controller calculates the compensation pressure using the theoretical hydraulic pressure compensation formula, performs self-diagnosis based on the compensation pressure, and triggers the self-diagnosis program only when the actual pressure deviation exceeds a specified threshold.

[0010] Furthermore, the theoretical hydraulic pressure compensation formula is as follows:

[0011] In the formula, P c To compensate for pressure; θ is the diffuser deployment angle; v is the vehicle speed; A is the effective cross-sectional area of ​​the hydraulic cylinder; m is the diffuser panel mass; μ is the motion drag coefficient; K is the aerodynamic load factor; g is the gravitational acceleration.

[0012] Furthermore, the controller calculates the heating power according to the dynamic heating power formula, performs gradient power allocation, and prioritizes heating the rotating nodes. The dynamic heating power formula is:

[0013] In the formula, Q h λ is the required heating power; λ is the thermal conductivity of the panel composite material; ΔT is the target thawing temperature difference; S is the effective heating area; t d η represents the allowable melting time; η is the insulation layer efficiency coefficient.

[0014] Secondly, the present invention provides a control method for a hydraulically driven antifreeze automotive active diffuser, based on the aforementioned hydraulically driven antifreeze automotive active diffuser, comprising: Vehicle commands are obtained by controlling the controller in the output mechanism; The controller controls the power output of the hydraulic pump in the control output mechanism based on the vehicle command, and controls the heating of the heating device; the output end of the hydraulic pump pushes pressurized liquid to the hydraulic rod through the hydraulic conduit, the hydraulic rod controls the rotation angle of the diffuser panel by extension and retraction, and the heating device heats the overall structure based on the controller.

[0015] Furthermore, the controller dynamically calculates the icing probability based on environmental parameters, and then determines the preheating program based on the icing probability. The preheating program is only activated when the icing probability exceeds a preset threshold. The formula for calculating the icing probability is:

[0016] In the formula, P f δ represents the probability of icing; T represents the ambient temperature; RH represents the relative humidity of the air; T0 represents the reference freezing point; α, β, and γ represent the material characteristic coefficients; δ t Weighted by the duration of sustained low temperature.

[0017] Furthermore, the controller calculates the compensation pressure using a theoretical hydraulic pressure compensation formula, and performs self-diagnosis based on the compensation pressure. The self-diagnosis program is triggered only when the actual pressure deviation exceeds a specified threshold. The theoretical hydraulic pressure compensation formula is:

[0018] In the formula, P c To compensate for pressure; θ is the diffuser deployment angle; v is the vehicle speed; A is the effective cross-sectional area of ​​the hydraulic cylinder; m is the diffuser panel mass; μ is the motion drag coefficient; K is the aerodynamic load factor; g is the gravitational acceleration.

[0019] Furthermore, the controller calculates the heating power according to the dynamic heating power formula, performs gradient power allocation, and prioritizes heating the rotating nodes. The dynamic heating power formula is:

[0020] In the formula, Q h λ is the required heating power; λ is the thermal conductivity of the panel composite material; ΔT is the target thawing temperature difference; S is the effective heating area; t d η represents the allowable melting time; η is the insulation layer efficiency coefficient.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: Compared to traditional electric motor drive structures, this solution offers the following advantages: First, it utilizes a heating device for heating and antifreeze functions. In frosty weather, if localized freezing occurs, basic functions can be maintained through heating. Second, it provides higher driving force. Compared to the fixed torque of a traditional electric motor, the hydraulic rod can output higher transmission force, making it easier to break ice and start the vehicle in frozen conditions. Third, it has low driving power, and once it reaches the predetermined position, no further energy is required to maintain its position, resulting in lower overall power consumption. Fourth, the hydraulic transmission structure is more adaptable to the environment. The active diffuser is located at the bottom of the car and is subject to significant dust, mud, and rainwater intrusion. Compared to traditional electric motor drive mechanisms, the hydraulic transmission structure is simpler and less prone to obstruction by foreign objects. Fifth, the hydraulic transmission structure occupies less space. The hydraulic pump can be positioned appropriately, and hydraulic fluid is transmitted via conduits. The main actuator is only a single hydraulic rod, resulting in a smaller overall space footprint compared to electric motor drive structures. Sixth, it offers high ease of maintenance and reliability, superior lubrication conditions, long component life, robust structure, and strong impact resistance and electromagnetic interference resistance. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, 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 undue limitation of the invention. In the drawings: Figure 1 An exploded view of a hydraulically driven antifreeze automotive active diffuser provided in an embodiment of the present invention; Figure 2 A right-side isometric view of a hydraulically driven antifreeze automotive active diffuser provided in an embodiment of the present invention; Figure 3 A left-side isometric view of a hydraulically driven antifreeze automotive active diffuser provided in an embodiment of the present invention; Figure 4 A side sectional view of a hydraulically driven antifreeze automotive active diffuser in its deployed state, provided as an embodiment of the present invention; Figure 5 This is a side sectional view of a hydraulically driven antifreeze automotive active diffuser in its recovery state, provided as an embodiment of the present invention.

[0023] In the diagram: 1. Control output mechanism; 2. Conduit; 3. Hydraulic rod; 4. Anti-collision beam; 5. Mounting base; 6. Pin; 7. Heating device; 8. Diffuser panel. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0025] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0026] Example: Please see Figure 1 , Figure 2 and Figure 3 This embodiment provides a hydraulically driven antifreeze automotive active diffuser, comprising the following main components: a control output mechanism 1, a conduit 2, a hydraulic rod 3, a crash beam 4, a mounting base 5, a pin 6, a heating device 7, and a diffuser panel 8, wherein: The control output mechanism 1, including a controller and a hydraulic pump, is used to control the hydraulic power output according to the vehicle instructions. The pressurized liquid is pushed to the hydraulic rod 3 through the hydraulic conduit 2 to realize the extension and retraction function of the hydraulic rod 3. The conduit 2 is used to connect the controller hydraulic pump assembly and the hydraulic rod 3 to transmit hydraulic power; In terms of drive, the hydraulic rod 3 receives hydraulic power from the conduit 2, extends when the hydraulic pressure is high, and retracts when the hydraulic pressure is low; in terms of structure, the hydraulic rod 3 connects the mounting base 5 and the diffuser panel 8, providing power for the movement of the diffuser panel 8. The anti-collision beam 4 is used to fix the mounting base 5; Mounting base 5 is used to connect the anti-collision beam 4 and the diffuser panel 8; The pin 6 is used to connect the following components to realize the rotating structure: first, the mounting base 5 and the diffuser panel 8; second, the diffuser panel 8 and the hydraulic rod 3; third, the hydraulic rod 3 and the mounting base 5; Heating device 7 is used to heat the overall structure to achieve thawing and ice melting in a frozen state; The diffuser panel 8 is connected to the hydraulic rod 3 and the mounting base 5. By extending and retracting the hydraulic rod 3, the position of the diffuser panel 8 can be changed steplessly to meet different wind resistance and passability requirements.

[0027] Please refer to Figure 4 and Figure 5 In this design, the active diffuser has a multi-angle hovering function; this example only shows two extreme states: Figure 4 This corresponds to the unfolded state of the diffuser panel 8, which is also the extended state of the hydraulic rod 3; Figure 5The diffuser panel 8 corresponds to the retracted state, which is also the shortened state of hydraulic rod 3. During parking or low-speed driving, such as when parking, reversing, or navigating obstacles, the diffuser is typically in the retracted state. This provides a sufficient departure angle and integrates seamlessly with the rear bumper assembly, resulting in a better appearance and overall aesthetics. During high-speed driving, better aerodynamic performance is often required, and the diffuser is in the deployed state, i.e., the extended state of hydraulic rod 3. This allows airflow under the vehicle to exit the body more quickly, reducing overall air resistance and, through Bernoulli's principle, providing downforce to increase high-speed stability.

[0028] Furthermore, the hydraulic rod 3 controls the rotation angle and movement of the diffuser panel 8 by extending and shortening. One end of the hydraulic rod 3 is connected to the fixed mounting base 5, and the other end is connected to the diffuser panel 8. Since the mounting base 5 is relatively stationary, the extension and shortening of the hydraulic rod 3 causes the diffuser panel 8 to rotate around the corresponding axis, achieving different hovering angles. The power for the hydraulic rod 3 comes from the control output mechanism 1. The controller receives commands from the vehicle, and the hydraulic pump supplies liquid to the hydraulic rod 3 through the conduit 2 to increase the pressure and extend the hydraulic rod 3; or, the hydraulic pump recovers liquid from the hydraulic rod 3 through the conduit 2 to decrease the pressure and shorten the hydraulic rod 3.

[0029] This solution also addresses the defrosting and ice-breaking conditions of the active diffuser. Under normal, unfrozen conditions, the hydraulic pump and corresponding hydraulic output are at a relatively low value, and the movement of the base plate is smooth. When resistance occurs, meaning the hydraulic value exceeds the typical value under unfrozen conditions, combined with the temperature information provided by the vehicle, it can be determined whether freezing or frost has occurred. In the event of freezing, activating the heating device 7 melts the ice and snow, reducing the opening force and hydraulic pressure to allow the diffuser to operate normally. It should be noted that the heating device 7 typically consists of a resistance wire and a corresponding heat-resistant plastic coating; heating is achieved by applying a specific current.

[0030] In practice, the vehicle will provide execution commands to the controller, including driving the hydraulic pump and the heating device 7 for de-icing. The hydraulic pump is connected to the controller via signal and power lines, receiving commands and electrical energy to drive the internal structure and output hydraulic power, which is transmitted to the hydraulic rod 3 through the conduit 2. The controller, hydraulic pump, and conduit 2 have no special requirements for the main motion actuators and can be arranged in suitable positions according to the vehicle layout requirements. The hydraulic rod 3, as the main motion and implementation component, is structurally connected at one end to the diffuser panel 8 and at the other end to the base, and is connected to the corresponding structure through a through shaft to ensure its rotation during movement. Its mounting base 5 is often a robust structure such as the anti-collision beam 4 or the rear bumper assembly. The heating device 7 receives electrical energy from the controller and heats the diffuser panel 8 through its internal resistance heating wire, which can quickly thaw the entire structure in frozen conditions, enabling normal use in freezing weather.

[0031] During the movement, the hydraulic rod 3 is extended by the hydraulic power from the conduit 2. Since one end is connected to the relatively fixed base, the other end will push the diffuser panel 8 to rotate downwards to achieve the effect of opening the diffuser.

[0032] During the heating process, the vehicle determines whether it is in a frozen state based on the ambient temperature and the hydraulic pressure during the hydraulic transmission process. If the ambient temperature is below zero degrees Celsius and the hydraulic pressure during the hydraulic transmission process is greater than the hydraulic pressure in the unfrozen state, it is determined to be in a frozen state. The controller releases a command, and the heating device 7 starts working, using resistance wire heating for defrosting and thawing. The process is repeated to check whether the hydraulic pressure returns to normal operating conditions, at which point the heating operation stops.

[0033] It should be noted that, in order to address the problems of failure risk in extreme environments, mechanical-aerodynamic coupling interference, and energy efficiency bottlenecks in traditional diffusers, this solution makes further improvements, specifically including the following: Traditional diffusers rely on a single temperature threshold to activate heating (e.g., 0°C), making it impossible to predict icing risks. This can lead to the hydraulic mechanism freezing and jamming during sudden cold snaps. This solution adds an icing risk prediction model to the existing heating and defrosting functions. The controller dynamically calculates P based on environmental parameters. f By advancing the response node to before freezing occurs, early intervention is achieved, addressing the issue of delayed passive de-icing. The formula for calculating the freezing probability is as follows:

[0034] In the formula, P fδ represents the icing probability (0~1 dimensionless, source: real-time calculation by the controller); T represents the ambient temperature (°C, source: vehicle environmental sensor); RH represents the relative humidity (%, source: humidity sensor); T0 represents the reference freezing point (preset value -2°C, source: laboratory calibration data); α, β, and γ are material characteristic coefficients (source: thermal conductivity experimental calibration of diffuser panel); δ t Weighted by the duration of sustained low temperatures (Source: Historical freezing event statistics). When P... f When the value is greater than 0.7, the controller starts the preheating program in advance to prevent the hydraulic mechanism from freezing.

[0035] Traditional hydraulic systems neglect the influence of pneumatic loads, making them prone to diffuser angle drift or hydraulic pressure fluctuations at high speeds due to airflow impact. This solution calculates compensation pressure using a controller that combines vehicle speed, angle, and material parameters. It adds dynamic pressure compensation to address hydraulic fluctuations when the diffuser is hovering at different angles, achieving real-time decoupling control of pneumatic load and mechanical resistance, eliminating control instability at high speeds. The theoretical hydraulic pressure compensation formula is:

[0036] In the formula, P c The compensation pressure is (MPa, source: hydraulic pump pressure sensor); θ is the diffuser deployment angle (°, source: angle sensor); v is the vehicle speed (m / s, source: vehicle CAN bus); A is the effective cross-sectional area of ​​the hydraulic cylinder ( (Source: Hydraulic rod design parameters); m is the diffuser panel mass (kg, source: component BOM); μ is the motion drag coefficient (source: bench test data); K is the aerodynamic load factor (source: wind tunnel test calibration); g is the gravitational acceleration. Real-time calculation of theoretical pressure P. c If the actual pressure deviation is greater than 15%, a self-diagnostic procedure is triggered to eliminate mechanical jamming or leakage faults.

[0037] Traditional heating devices operate at full power, resulting in up to 60% ineffective heat loss during de-icing (e.g., when heating non-critical structures). This solution addresses the high energy consumption of traditional heating methods by introducing a gradient heating strategy. The controller calculates the heating power and distributes it in a gradient manner, prioritizing heating of rotating nodes and concentrating energy on freezing-sensitive areas. This overcomes the "high energy consumption, low efficiency" de-icing mode. The dynamic heating power formula is:

[0038] In the formula, Q h λ is the required heating power (W, source: control module calculation); λ is the thermal conductivity of the panel composite material (W / m·K, source: material certification data); ΔT is the target thawing temperature difference (°C, preset value ΔT = ambient temperature + 10°C); S is the effective heating area ( (Source: CAD model data); t d Allowable melting time (s, source: user setting, default 120s); η is the insulation layer efficiency coefficient (source: thermal imaging experimental data). Combined with P f Dynamically adjust Q based on vehicle battery status h Prioritize heating key rotating nodes (such as the connection of pin 6).

[0039] This solution achieves proactive defensive heating through an icing probability model, enhancing preventative de-icing capabilities and avoiding mechanical delay damage caused by the "frozen response" of traditional solutions. Gradient power allocation reduces ineffective heat loss by 70%, optimizing system energy consumption and particularly improving the low-temperature range performance of new energy vehicles. The hydraulic compensation algorithm can distinguish between three types of anomalies: icing jamming, mechanical failure, and aerodynamic interference, resulting in more refined fault diagnosis and reduced misjudgment rate. By integrating multi-parameter coupled calculations such as vehicle speed, angle, and material properties, it adapts to complex working conditions, ensuring the control accuracy of the diffuser under alternating snow / ice melting road conditions.

[0040] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A hydraulically driven antifreeze automotive active diffuser, characterized in that, include: Control output mechanism (1): Installed on the upper part of the anti-collision beam (4), including a controller and a hydraulic pump. The controller controls the power output of the hydraulic pump according to the vehicle instructions. The output end of the hydraulic pump pushes the pressurized liquid to the hydraulic rod (3) through the hydraulic conduit (2). Mounting base (5): Installed on the lower part of the anti-collision beam (4), with the lower end rotatably connected to the diffuser panel (8); Hydraulic rod (3): Both ends are rotatably connected to the mounting base (5) and the diffuser panel (8) respectively, and the rotation angle of the diffuser panel (8) is controlled by extension and retraction; Heating device (7): Installed on the surface of the diffuser panel (8), it heats the entire structure based on the controller.

2. The hydraulically driven antifreeze automotive active diffuser according to claim 1, characterized in that, The controller dynamically calculates the icing probability based on environmental parameters, and then determines the preheating program based on the icing probability. The preheating program is only started when the icing probability exceeds a preset threshold.

3. The hydraulically driven antifreeze automotive active diffuser according to claim 2, characterized in that, The formula for calculating the icing probability is: In the formula, P f α represents the probability of icing; T represents the ambient temperature; RH represents the relative humidity of the air; T0 represents the reference freezing point; α, β, and γ represent the material characteristic coefficients. δ t Weighted by the duration of sustained low temperature.

4. The hydraulically driven antifreeze automotive active diffuser according to claim 1, characterized in that, The controller calculates the compensation pressure using the theoretical hydraulic pressure compensation formula, performs self-diagnosis based on the compensation pressure, and triggers the self-diagnosis program only when the actual pressure deviation exceeds a specified threshold.

5. The hydraulically driven antifreeze automotive active diffuser according to claim 4, characterized in that, The theoretical hydraulic pressure compensation formula is as follows: In the formula, P c To compensate for pressure; θ is the diffuser deployment angle; v is the vehicle speed; A is the effective cross-sectional area of ​​the hydraulic cylinder; m is the diffuser panel mass; μ is the motion drag coefficient; K is the aerodynamic load factor; g is the gravitational acceleration.

6. The hydraulically driven antifreeze automotive active diffuser according to claim 1, characterized in that, The controller calculates the heating power according to the dynamic heating power formula, performs gradient power allocation, and prioritizes heating the rotating nodes. The dynamic heating power formula is: In the formula, Q h λ is the required heating power; λ is the thermal conductivity of the panel composite material; ΔT is the target thawing temperature difference; S is the effective heating area; t d Allowed melting time; η is the efficiency coefficient of the insulation layer.

7. A control method for a hydraulically driven antifreeze active diffuser for automobiles, based on the hydraulically driven antifreeze active diffuser for automobiles according to any one of claims 1-6, comprising: Vehicle commands are obtained through the controller in the control output mechanism (1); The controller controls the power output of the hydraulic pump in the control output mechanism (1) based on the vehicle command, and controls the heating of the heating device (7); the output end of the hydraulic pump pushes pressurized liquid to the hydraulic rod (3) through the hydraulic conduit (2), the hydraulic rod (3) controls the rotation angle of the diffuser panel (8) by extension and retraction, and the heating device (7) heats the overall structure based on the controller.

8. The control method for a hydraulically driven antifreeze automotive active diffuser according to claim 7, characterized in that, The controller dynamically calculates the icing probability based on environmental parameters, and then determines the preheating program based on the icing probability. The preheating program is only initiated when the icing probability exceeds a preset threshold. The formula for calculating the icing probability is: In the formula, P f α represents the probability of icing; T represents the ambient temperature; RH represents the relative humidity of the air; T0 represents the reference freezing point; α, β, and γ represent the material characteristic coefficients. δ t Weighted by the duration of sustained low temperature.

9. The control method for a hydraulically driven antifreeze automotive active diffuser according to claim 7, characterized in that, The controller calculates the compensation pressure using a theoretical hydraulic pressure compensation formula, and performs self-diagnosis based on the compensation pressure. The self-diagnosis program is triggered only when the actual pressure deviation exceeds a specified threshold. The theoretical hydraulic pressure compensation formula is as follows: In the formula, P c To compensate for pressure; θ is the diffuser deployment angle; v is the vehicle speed; A is the effective cross-sectional area of ​​the hydraulic cylinder; m is the diffuser panel mass; μ is the motion drag coefficient; K is the aerodynamic load factor; g is the gravitational acceleration.

10. The control method for a hydraulically driven antifreeze automotive active diffuser according to claim 7, characterized in that, The controller calculates the heating power according to the dynamic heating power formula, performs gradient power allocation, and prioritizes heating the rotating nodes. The dynamic heating power formula is: In the formula, Q h λ is the required heating power; λ is the thermal conductivity of the panel composite material; ΔT is the target thawing temperature difference; S is the effective heating area; t d Allowed melting time; η is the efficiency coefficient of the insulation layer.

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