Design method for calculating filter ratio of filter element based on pollution control dynamic model

Abstract

The invention discloses a design method for calculating a filter element filter ratio based on a pollution control dynamic model, which comprises the following steps of: designing a reference value of the filter element filter ratio according to a target pollution degree grade of pollution control through an established hydraulic system pollution control dynamic balance equation and principle; according to the method, the filter design personnel are helped to achieve the purpose of optimal filter matching for the system, the design defect that the filter ratio is determined blindly is overcome, the error that the filter ratio climbs to the height frequently occurring in actual design practice is avoided, and a theoretical basis and technical guidance are provided for high-cost-performance filter performance design and manufacturing of the filter element.

Description

Technical Field

[0001] This invention belongs to the technical field of hydraulic filter element filtration performance design, specifically a design method for calculating the filter element filtration ratio based on a dynamic pollution control model. Based on the target contamination level for hydraulic system pollution control—the particle size and particle count limits of the NAS1638 grade—combined with the definition of the filter element filtration ratio and the influencing factors of actual operating conditions, a mathematical model for hydraulic system pollution control dynamic balance is used to calculate the nominal design value of the filter element filtration ratio, thereby achieving the optimal filter element filtration ratio design effect. Background Art

[0002] The pollution control effect of the hydraulic system depends on the nominal value of the filter ratio of the filter element. The best matching nominal value of the filter ratio can not only control the target contamination level of the hydraulic system, but also intercept and filter enough polluting particles and impurities to ensure long-term, stable and reliable operation of the equipment.

[0003] In the practice of filter element design, the nominal value of the filter element filtration ratio is usually determined by referring to literature materials and relying on empirical data or adopting surveying and imitation methods. This design method is prone to the following two situations: First, the nominal value of the filter element filtration ratio selected to reduce design costs is too small, that is, the filtration efficiency of the filter element is too low. Such a filter element cannot stably control the hydraulic system contamination level at an ideal level even if it is filtered and purified for a long time; second, blindly increasing the filter element filtration ratio makes the nominal value of the filtration ratio too large, that is, the filtration efficiency of the filter element is too high. Such a filter element is prone to clogging too quickly, which reduces the service life of the filter element and increases the maintenance cost.

[0004] The nominal filter ratio of a filter element must be consistent with the target contamination level of the hydraulic system. Different hydraulic systems require different contamination levels, so the filter ratio parameter must be designed based on the target contamination level and the system's contamination characteristics. Contamination levels are commonly expressed using either NAS1638 or ISO4406. These two standards correspond to each other and are both based on the particle size distribution per unit volume of fluid. NAS1638 is more widely used. NAS1638 grades are determined by the highest contamination level corresponding to the number concentration of particles of 5-15μm, 15-25μm, and 25-50μm per 100mL of fluid. Particles of 5-15μm typically have the highest concentration, so NAS1638 grades are generally defined based on the number of particles of 5-15μm. For example, NAS1638-6 (abbreviated as NAS6) specifies a particle count limit of 16,000 particles of 5-15μm per 100mL.

[0005] The target contamination level of the hydraulic system is the expected value for safe and reliable operation of the hydraulic equipment during its life cycle. It is a known contamination level. In other words, according to the NAS1638 level standard, the concentration of particles larger than x microns (such as 5μm or other size ranges) downstream of the filter can be obtained. If the contamination concentration of particles upstream of the filter is known, the filtration ratio β of the filter element configured in the hydraulic system can be calculated according to the definition of filtration ratio. x , that is, the ratio of the particle concentration of a certain particle size corresponding to the upstream pollution degree to the particle concentration of the particle size corresponding to the target pollution degree.

[0006] The concentration of particles upstream of the filter depends on the hydraulic system's contamination characteristics. The contamination level of the hydraulic system's working fluid, particles generated during operation, particles intruding from outside, the impact of operating flow under cyclic conditions, and the filter element's filtration and purification (filtration ratio) all influence the upstream particle concentration. As the hydraulic system's operating cycle increases, the filtration ratio gradually reduces the hydraulic system's contamination concentration over time, while other factors, such as wear-induced particles, increase the hydraulic system's contamination concentration over time. This "one reduction, one increase" effect on hydraulic system contamination is precisely the starting point for optimized design.

[0007] Assuming that the filtration performance of the filter element installed in the hydraulic system is optimal, the filtration ratio of the filter element will definitely be achieved during the pollution control process: the number of new particles generated by the hydraulic system per unit time and the number of particles intercepted by the filter element reach a dynamic balance, that is, "one reduction" is equal to "one increase", that is, the pollution control effect of the hydraulic system achieves a relatively stable "target pollution level" level.

[0008] Therefore, by establishing a dynamic balance model for hydraulic system pollution control and based on the particle number limit of the NAS1638 target contamination level required by the hydraulic system, the required filter element filtration ratio can be calculated, which serves as an important reference for the design of the corresponding hydraulic system filter element. Summary of the Invention

[0009] The purpose of the present invention is to provide a design method for calculating the filter element filtration ratio based on a dynamic model of pollution control. This method helps filter designers to achieve the best match between the filter and the hydraulic system. By utilizing the dynamic balance principle of hydraulic system pollution control and according to the target pollution level requirements of the hydraulic system pollution control, the nominal value of the filter element filtration ratio is designed to meet the needs of the hydraulic system.

[0010] To achieve the above-mentioned purpose, the present invention adopts the following technical solution, which is a design method for calculating the filtration ratio of a filter element based on a pollution control dynamic model, characterized by the following specific steps:

[0011] Step S1: During the normal operation cycle of the hydraulic system, while the contaminants in the oil are filtered and intercepted by the filter element, new contaminants are generated in the hydraulic system. As the number of flow cycles increases, the amount of contaminants generated per unit time and the amount of contaminants intercepted by the filter element per unit time will tend to a dynamic equilibrium state. At this time, the oil contamination level of the hydraulic system will be at a relatively stable level, that is, the target contamination level of pollution control will be achieved. Within a certain maintenance cycle of the hydraulic system, the rate of change of the hydraulic system oil particle concentration = particle generation rate + particle concentration per unit time before a certain cycle - particle concentration per unit time after a certain cycle. The dynamic equilibrium model of hydraulic system pollution control is established as follows:

[0012]

[0013] Where:

[0014] V—oil volume, unit: L;

[0015] —The rate of change of the concentration of particles larger than x microns, unit: particles / Lmin;

[0016] W—the generation rate of particles larger than x microns, unit: pieces / min;

[0017] M i-1 —The concentration of particles larger than x microns before a certain cycle upstream of the filter element, i = 1, 2, 3...n, unit: particles / L;

[0018] Q—working flow rate, unit: L / min;

[0019] β x —Filter element filtration ratio corresponding to particle size x microns;

[0020] N i —The concentration of particles larger than x microns after a certain cycle downstream of the filter element, i = 1, 2, 3...n, unit: particles / L;

[0021] When the amount of contaminants in the hydraulic system that are intercepted by the filter element per unit time is equal to the generation rate of contaminants in the hydraulic system: In the filter element filtration ratio β x Under the action of the filter element, the particle concentration of the hydraulic system no longer changes with the cycle time, and the particle concentration will tend to be stable. The pollution control of the hydraulic system reaches a dynamic balance as the filtration and purification time is extended. The particle concentration at the dynamic balance is the concentration N of particles larger than x microns after a certain cycle downstream of the filter element. i This is the target contamination level. Based on the simplified formula (1), the optimal filter ratio calculation model for the filter element in the hydraulic system is as follows:

[0022]

[0023] Assuming that the target contamination level of the hydraulic system, i.e. the contamination control level, is level * of NAS1638, and according to the NAS1638 level standard, the limit of the number of particles larger than x microns corresponding to level * is a per 100mL;

[0024] Step S2: Substitute the hydraulic system's working flow Q and the particle number limit of the target contamination level obtained in step S1 into formula (3) and calculate the number of particles larger than x microns downstream of the filter element N after unifying the numerical units. x , unit is pieces / min:

[0025] N x =10aQ (3)

[0026] Step S3: Measure or estimate the generation rate W of particles larger than x microns in the hydraulic system. The relationship between the generation rates of particles larger than x microns corresponding to different hydraulic systems is as follows:

[0027] Comparison table of the generation rate of particles larger than x microns corresponding to different hydraulic systems

[0028]

[0029] Step S4: Determine the concentration M of particles larger than x microns before a certain cycle upstream of the filter element in the hydraulic system i-1 , taking the initial contamination degree of the hydraulic system as a reference, the relationship between the initial contamination degrees of different hydraulic systems is as follows:

[0030] Comparison table of initial contamination levels for different hydraulic systems

[0031]

[0032] Step S5: According to formula (4), combined with the generation rate W value of particles larger than x microns corresponding to the specific hydraulic system and the concentration M of particles larger than x microns before a certain cycle upstream of the filter element, i-1 The value is used to calculate the number of particles M larger than x microns in the filter element. x , unit is pieces / min:

[0033] M x =W+M i-1 Q (4)

[0034] Finally, the optimal filtration ratio of the filter element in the hydraulic system is obtained according to formula (2).

[0035] Furthermore, in order to improve the filtration efficiency of the filter element, the calculated filtration ratio nominal reference value is multiplied by the safety factor k, and the value of k is as follows:

[0036] The value of safety factor k

[0037]

[0038] Furthermore, if the target pollution level is multi-size graded, the corresponding β is calculated for each size segment of the particle number limit in NAS1638. x value.

[0039] Furthermore, if the target contamination level is the ISO4406 level, convert the ISO4406 level to the NAS1638 level before performing design calculations. The number after subtracting 9 from the ISO4406 level greater than 5μm is the NAS1638 level. The comparison table between NAS1638 and ISO4406 particle contamination levels is as follows:

[0040] NAS1638 and ISO4406 particle contamination level comparison table

[0041]

[0042] The present invention has the following advantages and beneficial effects: the present invention can help filter designers to accurately calculate the filtration ratio when designing the filtration performance of the filter element in the hydraulic system, realize the optimization design of the filtration capacity, overcome the disadvantages of blindly designing the filtration ratio parameters, and avoid falling into the pursuit of high comparison β that often occurs in design practice. x The value trap provides theoretical basis and technical guidance for matching the best filter for hydraulic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a simplified system diagram of the dynamic balance model for hydraulic system pollution control. DETAILED DESCRIPTION

[0044] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0045] like Figure 1 The following is a simplified diagram of the system that helps create a dynamic balance model for hydraulic system pollution control. xThe filter element is placed in the hydraulic system filter. The oil volume of the hydraulic system is V, the flow rate is Q, and the number of flow cycles per unit time is Q / V. As long as the filter ratio of the hydraulic system filter element is designed effectively, the corresponding contaminant particles will be intercepted with each flow cycle. During the normal operation cycle of the hydraulic system, while the contaminant particles in the oil are filtered and intercepted by the filter element, new contaminant particles are generated in the hydraulic system, that is, the particle generation rate of a certain particle size W. The newly generated contaminant particles include internal wear particles from the oil pump, actuator, etc., and external intrusion particles. As the number of flow cycles (operating time) continues to increase, the amount of particles generated per unit time and the amount intercepted by the filter element per unit time will tend to a dynamic equilibrium state. At this time, the oil contamination level of the hydraulic system will be at a relatively stable level, that is, the target contamination level of pollution control will be achieved.

[0046] Combine Figure 1 The oil particle concentration at a certain point in the upstream pipeline of the filter is taken as the research object. The rate of change of the oil particle concentration at this point is conserved with the rate of change of the particle concentration of the oil volume V of the hydraulic system. Based on this conservation principle, a dynamic balance model of hydraulic system pollution control is established. That is, within a maintenance cycle of the hydraulic system, the rate of change of the oil particle concentration in the hydraulic system = particle generation rate + particle concentration per unit time before a certain cycle - particle concentration per unit time after a certain cycle. The corresponding mathematical equation of the pollution control dynamic balance model is shown in formula (1):

[0047]

[0048] Where:

[0049] V—oil volume, unit: L;

[0050] —The rate of change of the concentration of particles larger than x microns, unit: particles / Lmin;

[0051] W—the generation rate of particles larger than x microns (external intrusion + internal wear), unit: pieces / min;

[0052] M i-1 —The concentration of particles larger than x microns before a certain cycle upstream of the filter element (such as the initial contamination level), unit: pieces / L;

[0053] Q—working flow rate, unit: L / min;

[0054] β x —Filter element filtration ratio corresponding to particle size x microns;

[0055] N i —The concentration of particles larger than x microns after a certain cycle downstream of the filter element (such as the target contamination level), unit: particles / L.

[0056] The physical meaning of the hydraulic system pollution control dynamic balance model equation (1) is further explained as follows:

[0057] (1) It reflects the change of the concentration of pollutant particles in the entire hydraulic system over time; M i-1 Q is the concentration of particles larger than x microns per unit time at a certain i-1 cycle upstream of the filter element; β x N i Q is the concentration of particles larger than x microns per unit time after a certain i cycles upstream of the filter element, where N i <M i-1 The decrease in concentration is the amount of air intercepted by the filter element per unit time. In short, the contaminants in the hydraulic system are constantly generated and intercepted by the filter element during the circulation process. As long as the filter element has a certain filtration capacity, the change in particle concentration in the hydraulic system will gradually reach equilibrium with the length of the working cycle.

[0058] (2) Assuming that the hydraulic system does not have a filter, then β x =1, N i =M i-1 , then the change in the concentration of pollutant particles in the hydraulic system over time is the single particle generation rate W, that is, Obviously, without a filter in the hydraulic system, the generation rate of system pollution particles will become higher and higher, accelerating wear until failure occurs and the system stops running.

[0059] (3) When i=1, it indicates that the hydraulic system has completed the first cycle. At this time, M i-1 =M0, N i =N1, M0 is the initial pollution concentration before the hydraulic system cycle, and the initial pollution concentration is the highest pollution level; when i=2, the system completes the second cycle, at this time M i-1 =M1、N i = N2; then i = 3, 4...n continue to cycle and run continuously, the pollution concentration after each cycle is N i It gradually decreases under the action of filtration ratio. As the working cycle time of the hydraulic system continues to increase, N i Gradually reach the target pollution level N n .

[0060] (4) When the amount of pollutants intercepted by the filter element per unit time is equal to the rate of generation of pollutants in the hydraulic system: (The number of cycles is sufficient, such as i = n), then the filter element filtration ratio β xUnder the action of the system particle concentration no longer changes with the change of the cycle time, and the particle concentration will tend to be stable. This means that the hydraulic system pollution control achieves dynamic balance as the filtration and purification time is extended. The particle pollution concentration N at dynamic balance n This is the "target pollution level", and the desired optimal filtration ratio calculation formula (2) can be obtained by simplifying formula (1):

[0061]

[0062] The working flow Q in formula (2) is a known value, and the principles for selecting other parameters are as follows:

[0063] W is the generation rate of particles larger than x microns (external intrusion and internal wear). W is selected and determined based on system performance, reliability and working environment requirements. Unit: pieces / min;

[0064] M i-1 —Take M i-1 =M0, that is, the initial contamination concentration of particles larger than x microns, M0, is determined based on the system manufacturing process and oil type, unit: pieces / L;

[0065] N i — Take N i =N n , that is, the target pollution level N of hydraulic system pollution control n (design known value), unit: pieces / L;

[0066] β x —NAS pollution level is generally defined by the number of particles between 5 and 15 μm. That is, β5 is usually of more concern, which refers to the filtration ratio of the filter element for particles larger than 5 μm.

[0067] According to the established formula (2), the filter element filtration ratio is calculated by adopting the following technical solution. The specific steps are as follows:

[0068] Step S1: Assume that the target contamination level (i.e., contamination control level) of the hydraulic system is N of NAS n According to NAS1638 grade standard, the N n The particle number limit for the level corresponding to 5-15 μm (or other size segments) is a / 100 mL;

[0069] Step S2: Use the hydraulic system working flow Q and the target pollution level N obtained in step S1 n Substituting the particle number limit into formula (5), and unifying the volume mL in a to L, the number of particles N with a target contamination level greater than 5 μm (or other particle size) downstream of the filter element can be obtained. 5n (Unit: pieces / min):

[0070] N 5n =10 aQ (5)

[0071] Step S3: Measure or estimate the hydraulic system's contamination particle generation rate W. Due to the complexity of actual working conditions, it is necessary to conduct long-term monitoring of system performance and reliability or estimate based on an empirical database. To avoid distortion caused by designing too small a filtration ratio, the generation rate of particles larger than 5 μm, W, is ≥ 20,000 particles / min. Refer to Table 1 for selection:

[0072] Table 1 Pollution particle generation rate W

[0073]

[0074] Step S4: Determine the initial contamination concentration M0 of particles larger than 5μm when circulating upstream of the filter element. The initial contamination concentration M0 is generally the maximum contamination during the circulation process. The initial contamination level depends on the system design, manufacturing process and oil quality. The initial contamination level NAS of the hydraulic system can be selected by referring to Table 2:

[0075] Table 2 Initial contamination NAS level

[0076]

[0077]

[0078] Refer to the recommended initial contamination level in Table 2 and convert the NAS level into the initial contamination concentration M0. Take NAS level 9 as an example: According to the NAS1638 level standard, the particle count limit for level 9 corresponding to 5-15 μm (or other size segments) is 128,000 particles / 100 mL. Converting the volume mL to L gives the initial contamination concentration: M0 = 128 × 10 4 pcs / L;

[0079] Step S5: Take the hydraulic system of conventional engineering machinery as an example (M0=128×10 4 Counts / L), calculate the concentration of particles larger than 5 μm upstream of the filter element M5 (unit: counts / min), and calculate according to formula (6):

[0080] M5=W+M0Q=W+128×10 4 Q (6)

[0081] Step S6: Based on the above formula (6) and formula (5), the concentration of particles larger than 5 μm in the upstream and downstream of the filter element can be used to calculate the reference value of the design nominal value of β5, that is, β5 = M5 / N 5n ;

[0082] Step S7: To improve the filtration efficiency of the filter element, multiply the calculated filtration ratio nominal reference value by the safety factor k. Generally, k=2-5. The larger k is, the larger the designed filtration ratio is, the higher the filtration efficiency is, the faster the dynamic balance of pollution control is achieved, and the safer and more reliable the operation of the equipment system is. The safety factor k is taken from Table 3:

[0083] Table 3 Values of safety factor k

[0084]

[0085] Step S8: If the target contamination level is multi-size classification, calculate the corresponding particle size β for each size segment according to the particle number limit in NAS1638. x value;

[0086] Step S9: If the target contamination level is the ISO 4406 level, convert the ISO 4406 level to the NAS 1638 level before performing the design calculation. The number after subtracting 9 from the ISO 4406 level greater than 5μm is the NAS 1638 level. For example, for ISO 4406-15 / 12, 15-9=6, which corresponds to NAS 1638 level 6. The correspondence between the two is shown in Table 4 (which can also be found in relevant standard documents):

[0087] Table 4 Comparison of NAS1638 and ISO4406 particle contamination levels

[0088]

[0089] Step S10: Carry out necessary experimental verification and test the filtration ratio β using GB / T18853 or ISO16889 x The value meets the design requirements, and the pollution holding capacity is tested and evaluated to see whether it meets the requirements of life or maintenance cycle.

[0090] Example 1

[0091] The working flow Q of the hydraulic system of a certain mechanical equipment is 120L / min, the total oil volume V of the system is 300L, and the target contamination level of the hydraulic system pollution control is level 5 of NAS1638. Calculate the nominal reference value of the filter element filtration ratio design.

[0092] A design method for calculating the filtration ratio of a filter element based on a pollution control dynamic model includes the following specific steps:

[0093] Step S1: According to the 5-level requirement of the hydraulic system pollution control target contamination degree NAS1638, the limit value of the number of particles of 5-15 μm (NAS graded particle size range) corresponding to level 5 is: a=8000 / 100 mL;

[0094] Step S2: According to the formula (5) in step S2 of the technical solution of the invention, a = 8000 / 100mL and Q = 120L / min are substituted respectively to calculate the number of particles larger than 5μm per unit time downstream of the filter element when the system reaches the target contamination level. 5n for:

[0095] N 5n =10×8000×120=96×10 5 (pieces / min)

[0096] Step S3: Refer to Table 1 and take the system pollution particle generation rate W = 30000 particles / min. Refer to Table 2 and take the initial pollution level as NAS level 9, that is, M0 = 128×10 4 / L, according to the formula (6) in step S5 of the technical solution of the invention, substituting Q = 120L / min, the initial pollution concentration M5 of particles larger than 5μm upstream of the filter element can be calculated as:

[0097] M5=W+MQ=30000+128×10 4 ×120=1536.3×10 5 (pieces / min)

[0098] Step S4: According to the formula (β5=M5 / N in the technical solution step S6 5n ) Calculate the filtration ratio β5 of the filter element for removing particles larger than 5μm:

[0099] β5=M5 / N 5n =1536.3×10 5 / 96×10 5 =16;

[0100] Step S5: Referring to Table 3, introduce a safety factor. Considering the expensiveness of the equipment, take k=5 and modify the filtration ratio β5 to: β5=16×5=80;

[0101] Step S6: Based on the estimated filtration ratio, filter materials with β5 ≥ 80 are selected, and the filter material selection is finally determined by considering factors such as the filter material's dirt holding capacity, flow capacity, filter material price, and processability;

[0102] Step S7: If necessary, use GB / T18853 or ISO16889 test verification to comprehensively evaluate the effectiveness of the filter element's filtration performance and dirt holding capacity, and perform iterative optimization and improvement based on the test data.

[0103] Example 2

[0104] If the target contamination level in Case 1 is ISO 4406 level 15 / 12, according to the comparison table of NAS1638 and ISO 4406 particle contamination levels in step S9 of the technical solution, it can be found that ISO 4406-15 / 12 corresponds to NAS1638 level 6. Then, referring to the implementation steps of Implementation Case 1, the filtration ratio for 5μm particle size with the target contamination level of NAS6 can be calculated.

[0105] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. The design method for calculating the filter element filtration ratio based on the pollution control dynamic model is characterized by The specific steps are: Step S1: During the normal operation cycle of the hydraulic system, while the contaminants in the oil are filtered and intercepted by the filter element, new contaminants are generated in the hydraulic system. As the number of flow cycles increases, the amount of contaminants generated per unit time and the amount of contaminants intercepted by the filter element per unit time will tend to a dynamic equilibrium state. At this time, the oil contamination level of the hydraulic system will be at a relatively stable level, that is, the target contamination level of pollution control will be achieved. Within a certain maintenance cycle of the hydraulic system, the rate of change of the hydraulic system oil particle concentration = particle generation rate + particle concentration per unit time before a certain cycle - particle concentration per unit time after a certain cycle. The dynamic equilibrium model of hydraulic system pollution control is established as follows: Where: V—oil volume, unit: L; —The rate of change of the concentration of particles larger than x microns, unit: particles / Lmin; W—the generation rate of particles larger than x microns, unit: pieces / min; M i-1 —The concentration of particles larger than x microns before a certain cycle upstream of the filter element, i = 1, 2, 3...n, unit: particles / L; Q—working flow rate, unit: L / min; β x —Filter element filtration ratio corresponding to particle size x microns; N i —The concentration of particles larger than x microns after a certain cycle downstream of the filter element, i = 1, 2, 3...n, unit: particles / L; When the amount of contaminants in the hydraulic system that are intercepted by the filter element per unit time is equal to the generation rate of contaminants in the hydraulic system: In the filter element filtration ratio β x Under the action of the filter element, the particle concentration of the hydraulic system no longer changes with the cycle time, and the particle concentration will tend to be stable. The pollution control of the hydraulic system reaches a dynamic balance as the filtration and purification time is extended. The particle concentration at the dynamic balance is the concentration N of particles larger than x microns after a certain cycle downstream of the filter element. i This is the target contamination level. Based on the simplified formula (1), the optimal filter ratio calculation model for the filter element in the hydraulic system is as follows: Assuming that the target contamination level of the hydraulic system, i.e. the contamination control level, is level * of NAS1638, and according to the NAS1638 level standard, the limit of the number of particles larger than x microns corresponding to level * is a per 100mL; Step S2: Substitute the hydraulic system's working flow Q and the particle number limit of the target contamination level obtained in step S1 into formula (3) and calculate the number of particles larger than x microns downstream of the filter element N after unifying the numerical units. x , unit is pieces / min: N x =10aQ (3) Step S3: Measure or estimate the generation rate W of particles larger than x microns in the hydraulic system. The relationship between the generation rates of particles larger than x microns corresponding to different hydraulic systems is as follows: Comparison table of the generation rate of particles larger than x microns corresponding to different hydraulic systems Step S4: Determine the concentration M of particles larger than x microns before a certain cycle upstream of the filter element in the hydraulic system i-1 , taking the initial contamination degree of the hydraulic system as a reference, the relationship between the initial contamination degrees of different hydraulic systems is as follows: Comparison table of initial contamination levels for different hydraulic systems Step S5: According to formula (4), combined with the generation rate W value of particles larger than x microns corresponding to the specific hydraulic system and the concentration M of particles larger than x microns before a certain cycle upstream of the filter element, i-1 The value is used to calculate the number of particles M larger than x microns in the filter element. x , unit is pieces / min: M x =W+M i-1 Q (4) Finally, the optimal filtration ratio of the filter element in the hydraulic system is obtained according to formula (2).

2. The design method for calculating the filter element filtration ratio based on the pollution control dynamic model according to claim 1 is characterized in that: In order to improve the filtration efficiency of the filter element, the calculated filtration ratio nominal reference value is multiplied by the safety factor k. The value of k is as follows: The value of safety factor k 3. The design method for calculating the filter element filtration ratio based on a pollution control dynamic model according to claim 1, characterized in that: If the target pollution level is multi-size classification, calculate the corresponding β for each size segment of the particle number limit in NAS1638. x value.

4. The design method for calculating the filter element filtration ratio based on a pollution control dynamic model according to claim 1, characterized in that: If the target contamination level is the ISO4406 level, convert the ISO4406 level to the NAS1638 level before performing design calculations. The number after subtracting 9 from the ISO4406 level greater than 5μm is the NAS1638 level. The comparison table between NAS1638 and ISO4406 particle contamination levels is as follows: NAS1638 and ISO4406 particle contamination level comparison table

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