A design method for ultra-long life fluid devices

Abstract

This application provides a design method for an ultra-long-life fluid equipment, comprising the following steps: Step S1, performing active axial force balancing design, actively providing controllable electromagnetic axial force through the electromagnetic cooperation of the motor stator and rotor; Step S2, performing G2.5 level dynamic balancing precision control, treating the impeller and motor rotor as a single rotating assembly, and performing dynamic balancing design and correction on this single rotating assembly according to G2.5 level precision; Step S3, performing optimized bearing layout design, arranging the bearing assembly position near the comprehensive center of gravity of the shaft system's mass distribution; Step S4, performing lightweight shaft system design, reducing the weight of the impeller, motor rotor, and shaft through structural optimization and material selection while meeting strength and stiffness requirements. This application, through the synergistic effect of four key technologies, enables the actual service life of the fluid equipment to reach over 80,000 hours.

Description

Technical Field

[0001] This application relates to the field of fluid machinery design and manufacturing technology, and more specifically, to a method for designing ultra-long lifespan equipment such as centrifugal fans, axial fans, mixed-flow fans and pumps. Background Technology

[0002] Fluid equipment such as centrifugal fans, axial fans, mixed-flow fans, and various pumps are the most widely used rotating machinery in modern industry. Their core rotating components (including impellers, motor rotors, and shafts) are subjected to complex loads under high-speed operation, among which axial force and radial unbalanced force are the key bottlenecks restricting the service life of the equipment.

[0003] In existing technologies, the axial force in fluid equipment mainly originates from three aspects: first, the fluid axial force generated by the pressure difference between the front and rear impeller covers; second, the axial component of gravity generated by the rotor's own weight (especially in vertically installed equipment); and third, the electromagnetic axial force generated by the asymmetry of the motor's electromagnetic field. When the stator and rotor of the motor are not aligned, the air gap magnetic field will generate an axial component, causing the rotor to be subjected to an additional axial electromagnetic force. This force will significantly increase the axial load on the bearings and accelerate wear.

[0004] Furthermore, due to factors such as uneven material distribution, processing errors, and assembly errors, the rotating body inevitably suffers from uneven mass distribution. When the rotating body rotates at an angular velocity ω, a small eccentricity e will generate a huge centrifugal inertial force F=m·e·ω². These forces cannot cancel each other out, leading to equipment vibration, noise, and abnormal bearing wear. In existing technologies, pump impellers typically use a dynamic balancing accuracy of G6.3, which allows for a relatively large unbalance and is difficult to meet the requirements for ultra-long service life (over 80,000 hours).

[0005] The bearing's placement also affects equipment lifespan. When the bearing is not positioned near the center of gravity of the shaft system, the weight of the rotating body and centrifugal force will generate a significant additional torque load on the bearing. According to mechanical calculations, when rotating components rotate at 1500 rpm with an eccentricity of 1 mm, the centrifugal force alone can generate an additional load of approximately 170 N, significantly impacting bearing life.

[0006] Shaft weight is also a significant factor affecting bearing lifespan. According to the bearing life calculation formula L=(C / P)^p × 10 6 The life index (p) is calculated as follows: for ball bearings, p = 3; for roller bearings, p = 10 / 3. The larger the equivalent dynamic load P, the more exponentially the bearing life decreases. Heavier rotating bodies directly increase the P value, shortening bearing life. While there are attempts to reduce rotor weight using hollow structures in existing technologies, a systematic lightweight design principle to synergistically optimize life indexes has not yet been established.

[0007] In summary, the existing technology lacks a systematic design method that integrates axial force active balancing, high-precision dynamic balancing control, bearing optimization layout, and lightweight design, which makes it difficult for the actual service life of the equipment to break through the technical bottleneck of 80,000 hours. Summary of the Invention

[0008] This application aims to provide a design method for ultra-long life fluid equipment, which, through the synergistic effect of four key technologies, enables the actual service life of centrifugal fans, axial fans, mixed-flow fans, and pumps to reach more than 80,000 hours.

[0009] This application provides a design method for an ultra-long-life fluid device, which includes a centrifugal fan, an axial flow fan, a mixed flow fan, and a pump. The design method includes the following steps: Step S1, performing active axial force balancing design by actively providing controllable electromagnetic axial force through the electromagnetic cooperation of the motor stator and rotor to dynamically balance the fluid axial force generated by the impeller; Step S2, performing G2.5 level dynamic balancing precision control by treating the impeller and motor rotor as a whole rotating assembly and performing dynamic balancing design and correction on this whole rotating assembly according to G2.5 level precision; Step S3, performing optimized bearing layout design by arranging the bearing assembly position near the comprehensive center of gravity of the shaft system mass distribution; Step S4, performing lightweight shaft system design by reducing the weight of the impeller, motor rotor, and shaft through structural optimization and material selection while meeting strength and stiffness requirements; wherein, through the synergistic effect of the active axial force balancing design, the G2.5 level dynamic balancing precision control, the optimized bearing layout design, and the lightweight shaft system design, the actual service life of the fluid device reaches more than 80,000 hours.

[0010] In some embodiments, the axial force active balancing design in step S1 includes: step S11, establishing a fluid axial force calculation model for the impeller under operating conditions to determine the variation range of the fluid axial force; step S12, establishing an electromagnetic axial force model for the motor to determine the functional relationship between the electromagnetic axial force and the rotor axial displacement and excitation current; step S13, through the axial offset design of the stator magnetic poles or the configuration of the auxiliary excitation winding, enabling the motor to generate an electromagnetic axial force at the rated operating point that is opposite in direction and equal in magnitude to the fluid axial force; and step S14, using an axial displacement sensor and a servo control system to adjust the electromagnetic axial force in real time to dynamically track and balance the fluid axial force.

[0011] In some embodiments, the axial displacement sensor is used to monitor the axial position of the rotor in real time and transmit the monitoring signal to the servo control system, which adjusts the excitation current according to the monitoring signal to change the electromagnetic axial force.

[0012] In some embodiments, step S2, the G2.5 level dynamic balancing accuracy control includes: step S21, calculating the allowable imbalance of the overall rotating assembly at G2.5 level accuracy according to the ISO1940 standard; step S22, performing independent dynamic balancing correction on the impeller and motor rotor respectively, so that the imbalance of the individual components is better than G1 level; step S23, assembling the independently corrected impeller and motor rotor into the overall rotating assembly, and then performing overall dynamic balancing test and correction on the overall rotating assembly to ensure that the imbalance of the overall rotating assembly meets the G2.5 level requirements.

[0013] In some embodiments, the integral rotating assembly has a balance correction plane at the connection between the impeller and the motor rotor, and the overall dynamic balance test and correction are achieved by removing material on the balance correction plane.

[0014] In some embodiments, in step S3, the bearing optimization layout design includes: step S31, establishing a three-dimensional mass distribution model of the overall rotating assembly and calculating the overall center of gravity position of the entire rotating system; step S32, optimizing the configuration of the front and rear bearings according to the support span and bearing type, so that the overall center of gravity is located between the two bearing support points and as close as possible to the center point of the support span; step S33, calculating the equivalent dynamic load of the overall rotating assembly under different operating conditions and verifying whether the bearing life meets the design requirement of more than 80,000 hours.

[0015] In some embodiments, for vertically mounted fluid equipment, angular contact ball bearings are used to bear axial loads, and the assembly direction of the angular contact ball bearings is ensured to match the direction of the rotor's own weight.

[0016] In some embodiments, the lightweight design of the shaft system in step S4 includes: step S41, performing topology optimization on the impeller to remove redundant material; step S42, making the motor rotor adopt a hollow shaft structure, and reducing the wall thickness of the hollow shaft structure while meeting the requirements for torque transmission and critical speed; step S43, manufacturing the impeller and shaft using high-strength lightweight materials; and step S44, establishing a finite element model of the shaft system and verifying whether the critical speed, strength, and stiffness after the lightweight design meet the usage requirements.

[0017] In some embodiments, for large rotors, the hollow shaft structure is a segmented structure, which includes multiple hollow shaft segments connected by tie rods.

[0018] In some embodiments, the fluid device is any one of a centrifugal fan, an axial fan, a mixed-flow fan, or a centrifugal pump.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the disclosure of this application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating the design method of an ultra-long life fluid device according to this application is shown.

[0022] Figure 2 The diagram shows a flowchart of step S1 in the design method of an ultra-long life fluid device according to this application.

[0023] Figure 3 The diagram shows a flow chart of step S2 in the design method of an ultra-long life fluid device according to this application.

[0024] Figure 4 The diagram shows a flow chart of step S3 in the design method of an ultra-long life fluid device according to this application.

[0025] Figure 5 The diagram shows a flow chart of step S4 in the design method of an ultra-long life fluid device according to this application. Detailed Implementation

[0026] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0027] To enable those skilled in the art to better understand the solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0028] In the embodiments of this application, it should be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0029] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one…" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0030] In the description of the embodiments of this application, the words "example" or "for example" are used to indicate exemplification, illustration, or description. Any embodiment or design described as "example" or "for example" in the embodiments of this application is not to be construed as being more preferred or having more advantages than another embodiment or design. The use of the words "example" or "for example" is intended to present relative concepts in a clear manner.

[0031] In addition, "multiple" in the embodiments of this application refers to two or more. Therefore, "multiple" can also be understood as "at least two" in the embodiments of this application. "At least one" can be understood as one or more, such as one, two or more. For example, including at least one means including one, two or more and is not limited to which ones are included. For example, including at least one of A, B and C, then it can be A, B, C, A and B, A and C, B and C, or A and B and C.

[0032] It should be noted that in the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0033] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0034] This application provides a design method for an ultra-long-life fluid device, which includes a centrifugal fan, an axial flow fan, a mixed flow fan, and a pump, such as... Figure 1 As shown, the design method includes the following steps: Step S1, performing active axial force balancing design, actively providing controllable electromagnetic axial force through the electromagnetic cooperation of the motor stator and rotor to dynamically balance the fluid axial force generated by the impeller; Step S2, performing G2.5 level dynamic balancing precision control, treating the impeller and motor rotor as a whole rotating assembly, and performing dynamic balancing design and correction on this whole rotating assembly according to G2.5 level precision; Step S3, performing bearing optimization layout design, arranging the bearing assembly position near the comprehensive center of gravity of the shaft system mass distribution; Step S4, performing shaft system lightweight design, reducing the weight of the impeller, motor rotor, and shaft through structural optimization and material selection while meeting strength and stiffness requirements; wherein, through the synergistic effect of the active axial force balancing design, the G2.5 level dynamic balancing precision control, the bearing optimization layout design, and the shaft system lightweight design, the actual service life of the fluid equipment reaches more than 80,000 hours.

[0035] Through the synergistic effect of the above four steps, this application achieves the following: the active axial force balancing design significantly reduces axial load; the G2.5 level dynamic balancing precision control significantly reduces radial vibration load; the optimized bearing layout design makes the distribution of remaining load more balanced; and the lightweight shaft system design reduces the base value of all loads from the source. These four elements work together to enable the fluid equipment to achieve an actual service life of over 80,000 hours.

[0036] like Figure 2 As shown, in step S1, the active axial force balancing design includes: Step S11: Establish a calculation model of the fluid axial force of the impeller under working conditions to determine the range of variation of the fluid axial force; Step S12: Establish an electromagnetic axial force model of the motor to determine the functional relationship between the electromagnetic axial force and the rotor axial displacement and excitation current; Step S13: By designing the axial offset of the stator magnetic poles or configuring the auxiliary excitation winding, the motor generates the electromagnetic axial force at the rated operating point that is opposite in direction and equal in magnitude to the axial force of the fluid. Step S14: Using an axial displacement sensor and a servo control system, the electromagnetic axial force is adjusted in real time to dynamically track and balance the fluid axial force.

[0037] The axial displacement sensor is used to monitor the axial position of the rotor in real time and transmit the monitoring signal to the servo control system. The servo control system adjusts the excitation current according to the monitoring signal to change the electromagnetic axial force.

[0038] This application eliminates or significantly reduces the axial load on bearings through an active axial force balancing design. Its working principle is as follows: According to the principles of electrical machinery, when there is an axial misalignment between the stator and rotor magnetic center lines, the air gap magnetic field generates an axial component. This component exerts an axial electromagnetic force on the rotor, and the direction of this force always attempts to align the stator and rotor magnetic center lines. This application utilizes this physical principle by actively controlling the relative position of the stator and rotor magnetic center lines (e.g., axially offsetting the stator core relative to the rotor core), or by setting an auxiliary excitation winding and adjusting the excitation current, to actively generate a controllable electromagnetic axial force during motor operation. The direction of this electromagnetic axial force is designed to be opposite to the direction of the fluid axial force generated by the impeller. By real-time monitoring of the rotor axial displacement and closed-loop adjustment of the electromagnetic axial force, it dynamically tracks changes in the fluid axial force, thereby achieving real-time axial force balance. Through this step, the axial load on the bearing can be reduced by more than 60%, fundamentally solving the problem of premature bearing wear caused by axial force.

[0039] like Figure 3 As shown, in step S2, the G2.5 level dynamic balancing accuracy control includes: Step S21: Calculate the allowable imbalance of the integral rotating assembly at G2.5 accuracy according to ISO1940 standard; Step S22: Perform independent dynamic balancing correction on the impeller and motor rotor respectively, so that the imbalance of individual components is better than G1 level; Step S23: Assemble the independently calibrated impeller and motor rotor into the integral rotating assembly, and then perform an overall dynamic balance test and calibration on the integral rotating assembly to ensure that the imbalance of the integral rotating assembly meets the G2.5 level requirements.

[0040] The integral rotating assembly has a balance correction plane at the connection between the impeller and the motor rotor. The overall dynamic balance test and correction are achieved by removing material from the balance correction plane.

[0041] This application utilizes G2.5 level dynamic balancing precision control to minimize centrifugal inertial forces caused by uneven mass distribution, thereby reducing vibration and radial additional load on bearings. Its working principle is as follows: according to ISO 1940 standard, the dynamic balancing precision level G is proportional to the product of the rotor's center of mass eccentricity e and angular velocity ω (G = e·ω / 1000). G2.5 level means that after correction, the equivalent eccentric velocity of the rotor's center of mass is controlled below 2.5 mm / s. This invention designs and corrects the impeller and motor rotor as a single rotating assembly according to G2.5 precision, specifically including: first, independently dynamic balancing the impeller and motor rotor (achieving a level better than G1), then assembling them into a single rotating assembly, and finally performing overall dynamic balancing testing and correction. This "step-by-step + overall" strategy ensures that the imbalance of the final assembly is strictly controlled within the G2.5 level allowable range. Compared with the traditional G6.3 precision, the G2.5 precision reduces the unbalanced centrifugal force to less than 40% of the original and the vibration amplitude to more than 50%, significantly improving the working environment of the bearing.

[0042] like Figure 4 As shown, in step S3, the bearing optimization layout design includes: Step S31: Establish a three-dimensional mass distribution model of the overall rotating component and calculate the overall center of gravity position of the entire rotating system; Step S32: Optimize the position of the front and rear bearings according to the support span and bearing type, so that the overall center of gravity is located between the two bearing support points and as close as possible to the center point of the support span; Step S33: Calculate the equivalent dynamic load of the overall rotating assembly under different working conditions, and verify whether the bearing life meets the design requirement of more than 80,000 hours.

[0043] For vertically mounted fluid equipment, angular contact ball bearings are used to withstand axial loads, and it is ensured that the assembly direction of the angular contact ball bearing matches the direction of the rotor's own weight.

[0044] This application optimizes the bearing layout design to improve the stress state of the bearings, making the load on each bearing more balanced and avoiding local overload. Its working principle is based on the torque balance principle in mechanics: when the overall center of gravity of the rotating body is located between the two bearing support points and close to the span center, the torque generated by the rotor's own weight and residual unbalanced centrifugal force is evenly distributed to the two bearings, minimizing the additional torque load on any single bearing. This invention establishes a three-dimensional mass distribution model of the rotating components, accurately calculates the overall center of gravity position of the entire rotating system, including the impeller, motor rotor, shaft, and accessories, and then optimizes the configuration of the front and rear bearing support points based on this center of gravity position, so that the overall center of gravity is located between the two bearings and as close as possible to the span center. Through this optimization, the maximum bearing load can be reduced by more than 30%, and the bearing life is maximized due to load balance.

[0045] like Figure 5 As shown, in step S4, the lightweight design of the shaft system includes: Step S41: Perform topology optimization on the impeller to remove redundant material; Step S42: The motor rotor adopts a hollow shaft structure, and the wall thickness of the hollow shaft structure is reduced while meeting the requirements of torque transmission and critical speed. Step S43 involves manufacturing the impeller and shaft using high-strength, lightweight materials; Step S44: Establish the finite element model of the shaft system and verify whether the critical speed, strength and stiffness after the lightweight design meet the usage requirements.

[0046] For large rotors, the hollow shaft structure is a segmented structure, which includes multiple hollow shaft segments connected by tie rods.

[0047] This application reduces the basic load on the bearings from the source through lightweight shaft design. Its working principle is directly related to the bearing life calculation formula: L=(C / P)^p. The equivalent dynamic load P is synthesized from the radial load Fr and the axial load Fa. By reducing the mass of the rotating components, Fr (for horizontal shafts, Fr includes the rotor's own weight) and Fa (for vertical shafts, Fa includes the rotor's own weight) can be directly reduced. This invention achieves a weight reduction of 20%-35% while ensuring strength and rigidity by eliminating redundant material in the impeller through topology optimization, reducing the wall thickness of the rotor and shaft by using a hollow shaft structure, and replacing traditional steel with high-strength lightweight materials (such as aluminum alloys, titanium alloys, and composite materials). According to the bearing life formula, a 10% reduction in the equivalent dynamic load P can extend the ball bearing life by 37%, exponentially amplifying the lightweighting effect.

[0048] The fluid device is any one of a centrifugal fan, axial fan, mixed-flow fan, or centrifugal pump.

[0049] This application takes an industrial centrifugal fan as an example to illustrate the specific implementation process of this application. Its design goal is to enable the fan to run continuously for more than 80,000 hours under rated operating conditions.

[0050] Step S1: Perform active axial force balancing design.

[0051] First, a calculation model for the axial force of the centrifugal fan impeller under rated operating conditions (flow rate Q = 5000 m³ / h, total pressure P = 2000 Pa) was established through fluid dynamics calculations (CFD simulation). This model considered factors such as the pressure distribution of the front and rear shrouds of the impeller and leakage flow in the impeller cover sealing gap, and determined that the axial force generated by the impeller was F_axial = 285 N, with the direction pointing towards the air inlet.

[0052] Secondly, a mathematical model of the electromagnetic axial force F_em was established for the matching 15kW, 2950rpm 4-pole AC motor. According to Maxwell's stress tensor method, the electromagnetic axial force can be expressed as F_em = k·Φ²·δ, where k is a constant, Φ is the main air gap magnetic flux, and δ is the axial offset of the stator and rotor magnetic center lines. Through finite element electromagnetic field simulation, the functional relationship between F_em and the rotor axial displacement x and the excitation current I was accurately calibrated.

[0053] To achieve axial force balance, the stator core is axially offset by 1.5mm relative to the rotor core in the motor stator design. This offset design enables the motor to actively generate an electromagnetic axial force F_em that is opposite to the direction of the fluid axial force under rated excitation conditions, with a designed value in the range of 280-300N.

[0054] Meanwhile, an eddy current axial displacement sensor (such as...) is installed on the wind turbine casing near the rotor end. Figure 2 As shown in component 4, it is used to monitor the axial position of the rotor in real time, with a measurement accuracy of 0.01mm. The sensor signal is input to the PID controller ( Figure 2 (Part 5), the controller adjusts the excitation power supply ( Figure 2 The output current of component 6 dynamically changes the magnitude of the electromagnetic axial force. When the rotor experiences axial displacement due to fluctuations in operating conditions, the control system responds within 10ms, ensuring that the electromagnetic axial force tracks the changes in the fluid axial force in real time, guaranteeing the effective action on the bearing (…). Figure 2 The axial resultant force on the middle parts 7 and 8 is always kept within ±5N.

[0055] The effect of this step is that the axial load on the bearing is reduced from 285N to below 5N, a reduction of more than 98%, and the axial force can be ignored when calculating the bearing life.

[0056] Step S2: Perform G2.5 level dynamic balancing accuracy control.

[0057] According to the ISO 1940-1:2003 standard, the allowable unbalance calculation formula for G2.5 level accuracy is: m_per = (G × M) / (r × ω), where G = 2.5 g·mm / kg, M is the rotor mass (kg), r is the correction radius (m), and ω is the working angular velocity (rad / s).

[0058] Calculation process: The working angular velocity ω = 2π × 2950 / 60 = 308.8 rad / s; Impeller: M_imp=8.5kg, r_imp=0.15m → m_per = (2.5 × 8.5) / (0.15 ×308.8) = 0.458 g; Motor rotor: M_rot=12.3kg, r_rot=0.065m → m_per = (2.5 × 12.3) / (0.065 × 308.8) = 1.53 g; Implementation process: First, the impeller and motor rotor are dynamically balanced independently on a dynamic balancing machine. By removing material on a preset balance correction plane using a weight removal method, the remaining imbalance of a single component is better than 80% of the calculated value (i.e. better than 0.366g and 1.22g respectively), which is equivalent to G1 level accuracy.

[0059] Then, the independently calibrated impeller, motor rotor, and shaft were assembled into a single rotating assembly. This assembly was then mounted on a high-precision dynamic balancing machine for a dynamic balancing test at the operating speed. The test revealed a slight increase in overall imbalance due to assembly errors (such as keyway clearance and eccentricity of the stop fit). A minor weight reduction correction was then performed on the pre-reserved balancing planes on the impeller hub and motor rotor end faces, ultimately controlling the remaining imbalance of the entire rotating assembly to within 1.8 g·mm / kg (i.e., G1.8 grade), which is better than the G2.5 grade requirement.

[0060] The effect of this step is as follows: According to vibration theory, the unbalanced centrifugal force F = m·e·ω², where e is the equivalent eccentricity. The G2.5 level corresponds to e = 8.1 μm (at 2950 rpm), generating a centrifugal force of approximately 19.6 N (based on a total mass of 24 kg), which is only 40% of the traditional G6.3 level (e = 20.4 μm, centrifugal force 49.4 N). The effective vibration velocity is reduced from the traditional design of 4.5 mm / s to 1.8 mm / s, a reduction of 60%.

[0061] Step S3: Perform bearing optimization layout design.

[0062] Establish a three-dimensional mass distribution model of the overall rotating assembly, and accurately calculate the mass and center of gravity coordinates of each part (with the impeller inlet end face as the reference plane 0): Impeller: Mass 8.5kg, center of gravity L1=120mm; Shaft: Mass 3.2kg, center of gravity L2=200mm; Motor rotor: mass 12.3kg, center of gravity L3=280mm; Calculate the total centroid position G_total: Total mass M_total = 8.5 + 12.3 + 3.2 = 24.0 kg; Total mass moment Σ(M×L) = 8.5×120 + 12.3×280 + 3.2×200 = 1020 + 3444 +640 = 5104 kg·mm; The overall center of gravity position G_total = 5104 / 24.0 = 212.7 mm; Based on the bearing type (deep groove ball bearing) and the allowable support span (limited by housing size, maximum span 350mm), optimize the front and rear bearing positions: The front bearing (near the impeller) is located at L_front=120mm; The rear bearing is located at L_rear=420mm (span 300mm). At this point, the overall center of gravity G_total=212.7mm is located between the two bearings, 92.7mm from the front bearing and 207.3mm from the rear bearing.

[0063] The radial load on the two bearings is calculated based on the principle of torque balance: Assuming the rotor's weight is vertically downward, consider the most unfavorable operating condition (the rotor's center of gravity is in a horizontal position, and all gravity acts radially): F_front = M_total × g × (L_rear - G_total) / (L_rear - L_front) =24×9.8×(420-212.7) / (420-120) = 235.2 × 207.3 / 300 = 162.5 N; F_rear = M_total × g - F_front = 235.2 - 162.5 = 72.7 N; As can be seen, after optimization, the load ratio of the two bearings is 2.24:1. In contrast, if the rear bearing is placed at L_rear=500mm (span 380mm) according to the traditional design, then F_front = 235.2×(500-212.7) / 380 = 235.2×287.3 / 380 = 177.8 N, F_rear = 57.4 N, and the load ratio is 3.1:1. The optimized layout reduces the load on the far-end bearing (front bearing) by 8.6%.

[0064] The effect of this step is that by bringing the overall center of gravity closer to the support center, the additional torque caused by the center of gravity shift is reduced, resulting in a more balanced load distribution between the two bearings and preventing premature fatigue failure of one bearing. Simultaneously, since step S2 has reduced the unbalanced centrifugal force to an extremely low level, the alternating torque generated by the centrifugal force can be ignored in this step's calculations, simplifying the design.

[0065] Step S4: Perform lightweight design of the shaft system.

[0066] Lightweight design while ensuring strength and stiffness: Impeller topology optimization: Using the finite element method combined with topology optimization algorithms, the impeller was optimized with minimum compliance (maximum stiffness) as the objective and volume reduction as the constraint. Based on the optimization results, the blade thickness was reduced from 5mm to 3.5mm (maintaining 5mm at the blade root to ensure strength), and the crescent-shaped redundant material on the back side of the impeller disk was removed. After optimization, the impeller mass was reduced from 8.5kg to 7.0kg, a weight reduction of 17.6%. CFD verification showed that the aerodynamic performance did not decrease.

[0067] Hollow shaft structure for motor rotor: The original solid shaft is replaced with a hollow shaft, with an inner diameter / outer diameter ratio of 0.6. According to mechanics of materials, under the same torque, the weight per unit length of the hollow shaft is (1-(0.6)^4) = 1-0.1296 = 0.87, i.e., a weight reduction of 13%. Meanwhile, since the rotor laminations are mounted on the hollow shaft, the shaft diameter must ensure the critical speed requirement. Calculations show that after adopting the hollow shaft, the rotor assembly weight is reduced from 12.3 kg to 10.1 kg, a weight reduction of 17.9%.

[0068] Lightweight material for the shaft: The original shaft material was 45# steel (density 7.85g / cm³), now replaced with high-strength aluminum alloy 7075-T6 (density 2.81g / cm³, tensile strength 572MPa, higher than 45# steel's 600MPa, and with higher specific strength). Simultaneously, stainless steel sleeves are inlaid in the bearing positions and impeller mounting positions to meet surface hardness requirements. The shaft weight has been reduced from 3.2kg to 1.15kg, a weight reduction of 64%.

[0069] The total mass of the rotating assembly was reduced from 24.0 kg to 18.25 kg (7.0 + 10.1 + 1.15), a reduction of 24.0%. This is far superior to the 5-10% weight reduction of conventional designs.

[0070] The effect of this step is as follows: According to the bearing life formula L=(C / P)^p, the equivalent dynamic load P is proportional to the mass. A 24% weight reduction means a 24% reduction in the P value. For a ball bearing (p=3), the theoretical life is increased to 1 / (0.76)^3 = 2.28 times.

[0071] In the comprehensive analysis of life verification and synergistic effects, the 6209 type deep groove ball bearing was selected for the rear bearing, with a basic rated dynamic load. C = 35.1 kN. Calculate the equivalent dynamic load P, the radial load, which mainly consists of the rotor's self-weight and residual unbalanced centrifugal force. After quantification in step S4, the self-weight load is 18.25 × 9.8 / 2 (shared equally between the two bearings) = 89.4 N (calculated based on the optimized front bearing layout). The residual unbalanced centrifugal force is controlled within 19.6 N in step S2. Considering the worst-case scenario, the combined radial load Fr = 89.4 + 19.6 = 109 N. The axial load, after axial force balancing in step S1, Fa < 5 N, and can be ignored.

[0072] For deep groove ball bearings, when Fa / Fr ≤ e, P = Fr. Here, Fa / Fr ≈ 0, so we take P = Fr = 109 N.

[0073] Substitute into the lifespan calculation formula: L_h = (10^6 / (60n)) × (C / P)^³ = (10^6 / (60×2950)) × (35100 / 109)^³ = 5.65 × (322)^³ = 5.65 × 33,376,648 = 1.886 × 10^8 hours Its computing lifespan reaches 188 million hours, far exceeding the design target of 80,000 hours.

[0074] Synergistic Effect Analysis: The above calculations intuitively demonstrate the synergistic effect of the four steps. If only lightweighting is performed (without axial force balancing or high-precision dynamic balancing), then P≈ axial force 285N + self-weight load 89.4N = 374.4N, and the lifespan L_h = 5.65 × (35100 / 374.4)^³ = 5.65 × (93.75)^³ = 5.65 × 824,000 = 4.66 × 10^6 hours, or 466,000 hours, which still meets the 80,000-hour requirement, but the operating quality, such as vibration and noise, is poor. However, this invention, through the synergy of the four steps, reduces the P value from 374.4N to 109N, and increases the lifespan from 466,000 hours to 188 million hours, an increase of 403 times. This is precisely the exponential synergistic effect produced by the "synergistic effect".

[0075] This application uses an axial flow fan for a cooling tower as an example, with a design target of 80,000 hours. The main characteristics of an axial flow fan are high flow rate, low static pressure, and relatively small axial force, but the fan diameter is large and the dynamic balance requirement is high.

[0076] The design method adopted in this application includes: For active axial force balancing, a magnetic field-oriented control strategy of a permanent magnet synchronous motor is used to generate a controllable electromagnetic axial force through the d-axis current, which balances the impeller axial force; for dynamic balancing, the large-diameter axial flow impeller adopts G2.5 level precision control, and special balancing correction is performed for composite material blades; for bearing layout, considering the cantilever installation characteristics of axial flow fans, a double bearing close arrangement is adopted to make the impeller center of gravity as close as possible to the bearing support point; for lightweighting, carbon fiber composite materials are used to manufacture the blades, reducing weight by 40% compared to aluminum alloy blades.

[0077] Design verification shows that the axial flow fan has a calculated lifespan of 120,000 hours, meeting the 80,000-hour requirement.

[0078] This application takes the design of a mixed-flow fan as an example. The mixed-flow fan combines the characteristics of large air volume of an axial flow fan and high static pressure of a centrifugal fan, and the impeller is subjected to complex stress.

[0079] The method described in this application focuses on solving the coupling problem of axial and radial forces in the three-dimensional flow field of a mixed-flow impeller. The variation law of axial force under different operating conditions is accurately obtained through CFD calculations, and corresponding electromagnetic axial force compensation curves are designed. Dynamic balancing control adopts G2.5 level, and the influence of aeroelastic deformation of the impeller under high-speed rotation on the equilibrium state is considered.

[0080] Actual testing showed that after 92,000 hours of continuous operation, the bearing wear of the mixed-flow fan designed using this invention remained within the allowable range, achieving the design target.

[0081] This embodiment uses an industrial centrifugal pump as an example, with a design target of 80,000 hours. The axial force of pump equipment mainly comes from the pressure difference between the front and rear cover plates of the impeller, and varies significantly with the flow rate.

[0082] Using the method described in this application, an auxiliary thrust electromagnetic device is installed at the end of the motor to adjust the reverse thrust in real time according to the pump's operating conditions. For dynamic balance control, the pump impeller and motor rotor are controlled at G2.5 level and connected using a diaphragm coupling to reduce misalignment. Regarding bearing layout, considering the pump's cantilever structure, double bearings are used for support and are positioned as close as possible to the impeller's rear end. For weight reduction, the impeller is precision cast and machined on five axes, eliminating redundant material and reducing weight by 15%.

[0083] Based on bearing life calculations, the selected bearings meet the 80,000-hour life requirement. After 8,600 hours of actual bench testing (equivalent accelerated testing), the bearings are in good condition and are expected to meet the design life.

[0084] The core of this application lies in the fact that the four technical methods are not simply superimposed, but rather form a deep technological synergy. Specifically: The axial force balance and lightweight design are achieved in synergy. The lightweight design reduces the weight of the rotor, which reduces the "interference forces" (such as the rotor's own weight component) that the axial force active balancing system needs to balance in addition to the fluid axial force. This reduces the adjustment burden of the electromagnetic axial force, making the balance control more precise and faster in response.

[0085] The synergy between dynamic balancing and bearing layout is achieved. The G2.5 grade high-precision dynamic balancing reduces the residual imbalance to an extremely low level. This allows for a smaller safety factor when calculating the torque generated by the residual imbalance centrifugal force during bearing layout optimization design. This enables the bearings to be arranged closer to the theoretical optimal position, further optimizing the load distribution.

[0086] The design achieves a synergy between lightweighting and dynamic balancing. The lightweight design reduces the mass of the rotating components. According to the centrifugal force formula F=m·e·ω², under the same residual eccentricity e, the reduction in mass m directly reduces the unbalanced centrifugal force F. In other words, lightweighting creates more favorable conditions for achieving G2.5 level dynamic balancing, or rather, it reduces the difficulty of achieving G2.5 level accuracy.

[0087] This approach achieves a combined effect of four factors on bearing life, as revealed by the bearing life formula L=(C / P)^p. Here, P is a comprehensive equivalent dynamic load comprising axial force, radial force, and torque. Axial force balancing directly reduces the axial component of P; dynamic balance control and bearing layout optimization reduce the radial and torque components of P; and weight reduction simultaneously reduces the base values ​​of both the axial and radial components. This four-pronged approach causes P to decrease geometrically, leading to an exponential increase in bearing life L, ultimately breaking through the 80,000-hour technical bottleneck.

[0088] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Although this application has disclosed preferred embodiments as above, it is not intended to limit this application. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this application. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A design method for an ultra-long life fluid device, the fluid device comprising a centrifugal fan, an axial flow fan, a mixed flow fan, and a pump, characterized in that, The design method includes the following steps: Step S1 involves performing an active axial force balancing design. This design utilizes the electromagnetic interaction between the motor stator and rotor to actively provide a controllable electromagnetic axial force, thereby dynamically balancing the fluid axial force generated by the impeller. Step S2: Perform G2.5 level dynamic balancing accuracy control, treat the impeller and motor rotor as a whole rotating assembly, and perform dynamic balancing design and correction on the whole rotating assembly according to G2.5 level accuracy; Step S3: Perform bearing optimization layout design, and arrange the bearing assembly position near the overall center of gravity of the shaft system mass distribution; Step S4: Perform lightweight shaft design. While meeting the strength and stiffness requirements, reduce the weight of the impeller, motor rotor and shaft through structural optimization and material selection. The synergistic effect of the axial force active balancing design, the G2.5 level dynamic balancing precision control, the optimized bearing layout design, and the lightweight shaft system design enables the actual service life of the fluid equipment to reach more than 80,000 hours.

2. The design method according to claim 1, characterized in that: In step S1, the active axial force balancing design includes: Step S11: Establish a calculation model of the fluid axial force of the impeller under working conditions to determine the range of variation of the fluid axial force; Step S12: Establish an electromagnetic axial force model of the motor to determine the functional relationship between the electromagnetic axial force and the rotor axial displacement and excitation current; Step S13: By designing the axial offset of the stator magnetic poles or configuring the auxiliary excitation winding, the motor generates the electromagnetic axial force at the rated operating point that is opposite in direction and equal in magnitude to the axial force of the fluid. Step S14: Using an axial displacement sensor and a servo control system, the electromagnetic axial force is adjusted in real time to dynamically track and balance the fluid axial force.

3. The design method according to claim 2, characterized in that: The axial displacement sensor is used to monitor the axial position of the rotor in real time and transmit the monitoring signal to the servo control system. The servo control system adjusts the excitation current according to the monitoring signal to change the electromagnetic axial force.

4. The design method according to claim 1, characterized in that: In step S2, the G2.5 level dynamic balancing accuracy control includes: Step S21: Calculate the allowable imbalance of the integral rotating assembly at G2.5 accuracy according to ISO1940 standard; Step S22: Perform independent dynamic balancing correction on the impeller and motor rotor respectively, so that the imbalance of individual components is better than G1 level; Step S23: Assemble the independently calibrated impeller and motor rotor into the integral rotating assembly, and then perform an overall dynamic balance test and calibration on the integral rotating assembly to ensure that the imbalance of the integral rotating assembly meets the G2.5 level requirements.

5. The design method according to claim 4, characterized in that: The integral rotating assembly has a balance correction plane at the connection between the impeller and the motor rotor. The overall dynamic balance test and correction are achieved by removing material from the balance correction plane.

6. The design method according to claim 1, characterized in that: In step S3, the optimized bearing layout design includes: Step S31: Establish a three-dimensional mass distribution model of the overall rotating component and calculate the overall center of gravity position of the entire rotating system; Step S32: Optimize the position of the front and rear bearings according to the support span and bearing type, so that the overall center of gravity is located between the two bearing support points and as close as possible to the center point of the support span; Step S33: Calculate the equivalent dynamic load of the overall rotating assembly under different working conditions, and verify whether the bearing life meets the design requirement of more than 80,000 hours.

7. The design method according to claim 6, characterized in that, For vertically mounted fluid equipment, angular contact ball bearings are used to withstand axial loads, and it is ensured that the assembly direction of the angular contact ball bearing matches the direction of the rotor's own weight.

8. The design method according to claim 1, characterized in that, In step S4, the lightweight design of the shaft system includes: Step S41: Perform topology optimization on the impeller to remove redundant material; Step S42: The motor rotor adopts a hollow shaft structure, and the wall thickness of the hollow shaft structure is reduced while meeting the requirements of torque transmission and critical speed. Step S43: The impeller and shaft are manufactured using high-strength, lightweight materials; Step S44: Establish the finite element model of the shaft system and verify whether the critical speed, strength and stiffness after the lightweight design meet the usage requirements.

9. The design method according to claim 8, characterized in that, For large rotors, the hollow shaft structure is a segmented structure, which includes multiple hollow shaft segments connected by tie rods.

10. The design method according to any one of claims 1 to 9, characterized in that, The fluid device is any one of a centrifugal fan, axial fan, mixed-flow fan, or centrifugal pump.

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