A method for measuring, calculating and evaluating the vibration and noise of an electric cooling fan

Abstract

The present invention provides a method for calculating and evaluating the vibration and noise of an electric cooling fan, which can calculate the vibration and noise level of the fan at the design stage and evaluate the vibration and noise level of the electric cooling fan, so as to determine whether the vibration and noise level of the electric cooling fan meets the vehicle vibration and noise performance requirements, so as to control and adjust the vibration and noise level of the fan in time at the design stage of the electric cooling fan. The electric cooling fan enterprise can complete the calculation and evaluation of the vibration and noise level of the electric cooling fan in its own laboratory without relying on vehicle test data, greatly improving the verification efficiency, avoiding mold repair and re-molding, solving the problem that it is not easy to change the electric cooling fan mold after it is finalized, saving time and reducing the development cost of the fan and the vehicle. The calculation and evaluation method of the present invention can be applied to electric cooling fans in new energy fields such as ordinary fuel vehicles, pure electric vehicles, and hybrid vehicles.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive parts and relates to a method for measuring and evaluating part parameters. Background Art

[0002] The electric cooling fan is one of the important components to ensure the normal operation of the automotive engine. Its main function is to generate a pressure difference before and after the engine cooling module to promote air circulation, enhance the heat dissipation capacity of the heat exchanger, and ensure the air flow demand of the whole vehicle under certain special working conditions such as urban idling and mountain climbing. Since the electric cooling fan is a rotating part, the noise and vibration generated by the fan rotation will be transmitted to the cockpit through the vehicle body, causing complaints from the passengers. Therefore, it is particularly important to control the vibration and noise of the cooling fan.

[0003] However, at present, it is rarely possible to accurately determine whether the vibration and noise level of the fan meets the vibration and noise performance requirements of the whole vehicle at the design stage. Even if the vibration and noise level of the fan is evaluated, it is only based on fuzzy empirical values, with low reliability. Therefore, once the vehicle is assembled for the whole vehicle test, the vibration and noise of the electric cooling fan may often not meet the vibration and noise performance requirements of the whole vehicle. As a result, the structure of the electric cooling fan needs to be adjusted, and its mold needs to be repaired or even remade, wasting a lot of time and increasing the development cost of the fan and the whole vehicle. Summary of the Invention

[0004] To solve the problems described in the background art, the present invention proposes a method for measuring and evaluating the vibration and noise of an electric cooling fan.

[0005] The measurement and evaluation method of the present invention includes the following steps:

[0006] Step 1: Obtain the rotational speed-stiction force value data of the electric cooling fan;

[0007] Step 2: Fit the rotational speed-stiction force value data of the electric cooling fan to obtain a stiction force target formula and a stiction force measurement formula;

[0008] Step 3: Calculate the stiction force measurement values of the designed electric cooling fan at different rotational speeds through the stiction force measurement formula;

[0009] Step 4: Generate a stiction force measurement curve based on the rotational speed-stiction force measurement values, generate a stiction force target curve based on the stiction force target formula, and compare the stiction force measurement curve with the stiction force target curve: if the stiction force measurement value is less than or equal to the stiction force target value, the designed electric cooling fan meets the vibration and noise requirements of the whole vehicle; if the stiction force measurement value is greater than the stiction force target value, the designed electric cooling fan does not meet the vibration and noise requirements of the whole vehicle.

[0010] Further, in the first step, select multiple electric cooling fans that can meet the vehicle vibration and noise requirements within the used speed range. Install the electric cooling fans on a rigid bench through multiple mounting and fixing points on the air shroud. Install force sensors at the mounting positions of multiple mounting and fixing points on the bench. Connect the force sensors to a charge amplifier, connect the speed sensor of the electric cooling fan to a speed signal converter, and connect both the charge amplifier and the speed signal converter to a computer. Measure the stalling force value of the electric cooling fan under different speed conditions.

[0011] Further, under different speed conditions, measure the vibration forces in the X, Y, and Z directions at the mounting and fixing points of each electric cooling fan through the force sensors, and calculate the stalling force value of the electric cooling fan based on the vibration forces in the X, Y, and Z directions at the mounting and fixing points of each electric cooling fan.

[0012] Further, in the second step, fit the speed-stalling force value data of multiple electric cooling fans to obtain a stalling force target formula: when the speed of the electric cooling fan is less than or equal to a specific speed, its stalling force target value is a fixed value; when the speed of the electric cooling fan is greater than the specific speed, its stalling force target value increases linearly with the speed.

[0013] Further, the stalling force target formula is obtained through matlab software combined with the least squares method:

[0014] 0 < X ≤ 1200 RPM, F m = a N,

[0015] X > 1200 RPM, F m = (b * X - c) N,

[0016] where X is the speed, and F m is the stalling force target value, and a, b, and c are all constants.

[0017] Even further, in the second step, fit the speed-stalling force value data of each electric cooling fan, use the Gaussian function probability density function to obtain a fitting formula, and verify the effectiveness of the fitting formula through the parameters of the electric cooling fan until the effectiveness meets the requirements to obtain a stalling force calculation formula.

[0018] Even further, the fitting formula is obtained through the infinite approximation of three Gaussian functions and the fitting with matlab software combined with the least squares method:

[0019]

[0020]

[0021]

[0022] wherein, a 1 is the maximum allowable unbalance of the electric cooling fan, with the unit of g.mm; m 1 is the rotational speed of the first-order natural frequency, with the unit of r / min; m 2 is the rotational speed of the second-order natural frequency, with the unit of r / min; m 3 is the rotational speed of the third-order natural frequency, with the unit of r / min; S 1 is the variance of the rotational speed of the first-order natural frequency, with the unit of r / min; S 2 is the variance of the rotational speed of the second-order natural frequency, with the unit of r / min; S 3 is the variance of the rotational speed of the third-order natural frequency, with the unit of r / min; X is the rotational speed, with the unit of RPM; F c is the measured value of the jamming force, with the unit of N;

[0023] And the effectiveness of the fitting formula is verified by the parameters of the electric cooling fan until the effectiveness meets the requirements, and the measured formula of the jamming force is obtained.

[0024] Furthermore, in the above-mentioned effectiveness verification, the maximum allowable unbalance of the measured electric cooling fan is determined according to the industrialization ability, and the data of the measured electric cooling fan is analyzed by using CAE software to obtain the natural frequencies of each order and their variances of the electric cooling fan, and substituting them into the fitting formula to calculate the measured value of the jamming force, and the effectiveness of the fitting formula is verified by comparing the measured value of the jamming force with the calculated value of the jamming force under the same rotational speed condition of the measured electric cooling fan.

[0025] Even further, in the above-mentioned effectiveness verification, for the measured electric cooling fan, under the same rotational speed condition, if the tolerance range between the calculated value of the jamming force by the fitting formula and the measured value of the jamming force ≤ ±5%, the effectiveness of the fitting formula meets the requirements.

[0026] Even further, the measurement and evaluation method of the present invention further includes: Step Five: If the designed electric cooling fan does not meet the requirements of the vehicle's vibration and noise, by increasing the stiffness of the electric cooling fan and increasing the natural frequency of the electric cooling fan, the changed maximum allowable unbalance and the natural frequencies of each order and their variances are obtained;

[0027] Step Six: Repeat Step Three to Step Five until the changed electric cooling fan meets the requirements of the vehicle's vibration and noise.

[0028] Compared with the prior art, the present invention can measure the vibration and noise level of the fan during the design stage and evaluate the vibration and noise level of the electric cooling fan, so as to determine whether the vibration and noise level of the electric cooling fan meets the requirements of the vehicle's vibration and noise performance. In this way, the vibration and noise level of the fan can be controlled and adjusted in a timely manner during the design stage of the electric cooling fan. The enterprise of electric cooling fans can complete the measurement and evaluation of the vibration and noise level of the electric cooling fan in its own laboratory without relying on the vehicle test data, which greatly improves the verification efficiency, avoids mold repair and re-molding, solves the problem that it is not easy to change the mold of the electric cooling fan after the mold is finalized, saves time, and reduces the development cycle and cost of the fan and the vehicle. The measurement and evaluation method of the present invention can be applied to the electric cooling fans in new energy fields such as ordinary fuel vehicles, pure electric vehicles, and hybrid vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 FIG. is a schematic diagram of the stalling force test device for the electric cooling fan.

[0030] Figure 2 FIG. is the target curve of the stalling force and the measured value curve of the stalling force of the electric cooling fan.

[0031] Figure 3 FIG. is the target curve of the stalling force and the calculated curve of the stalling force of the improved electric cooling fan. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following will describe in detail the embodiments of the present invention with reference to the drawings. However, they do not constitute a limitation to the present invention, but are only for illustration purposes. At the same time, through the description, the advantages of the present invention will be more clearly understood. All deformations that can be directly derived or associated by those of ordinary skill in the art from the content disclosed in the present invention shall be considered as within the protection scope of the present invention. The positional relationships described in the embodiments are consistent with those shown in the drawings. Other parts not described in detail in the embodiments are all prior art.

[0033] As Figure 1As shown, when the electric cooling fan T needs to be tested, it is installed on a rigid bench through four mounting and fixing points T1, T2, T3, and T4 on the air shroud. Since the excitation force during the high-speed rotation of the electric cooling fan is very large, in order to eliminate the measurement error caused by the deformation of the environmental components and accurately measure the stalling force generated by the electric cooling fan body, a rigid bench with very small deformation or even negligible deformation is selected; the electric cooling fan is connected to the bench by bolts, and the force sensor is also connected to the bench by bolts. A force sensor is arranged at the installation position of each mounting and fixing point on the bench. One force sensor leads out three connecting wires to measure the vibration forces in the X, Y, and Z directions respectively. Connect the force sensor to a charge amplifier, connect the rotational speed sensor of the electric cooling fan T to a rotational speed signal converter, and connect both the charge amplifier and the rotational speed signal converter to a computer to complete the installation of the test device.

[0034] In this embodiment, 30 electric cooling fans are selected. These 30 electric cooling fans can meet the requirements of vehicle vibration and noise within the operating rotational speed range. Measure them through the above experimental device. Measure the vibration forces in the X, Y, and Z directions at the four mounting and fixing points of the electric cooling fan through the force sensors. The stalling force of the electric cooling fan is the resultant force of the vibration forces in the X, Y, and Z directions at the four mounting and fixing points. Then the stalling force of the electric cooling fan is:

[0035]

[0036] Among them, F is the stalling force, F 1 is the resultant force of the vibration forces in the X direction at the 4 mounting and fixing points, F 2 is the resultant force of the vibration forces in the Y direction at the 4 mounting and fixing points, F 3 is the resultant force of the vibration forces in the Z direction at the 4 mounting and fixing points.

[0037] Map the curve of the stalling force varying with the rotational speed through the software of the vibration and noise measurement and analysis system.

[0038] Fit the 30 groups of rotational speed-stalling force value data to obtain the target curve of the stalling force as shown by the dotted line in Figure 2 and obtain the target formula of the stalling force through the matlab software combined with the least squares method:

[0039] 0 < X ≤ 1200 RPM, F m = 1.732 N,

[0040] X > 1200 RPM, F m = (0.00433 * X - 3.47) N,

[0041] where X is the rotational speed and F m is the target value of the stalling force.

[0042] During the operation of an electric cooling fan, in the ideal case without resonance, the stiction force increases linearly with the rotational speed. However, in reality, an electric cooling fan has a natural frequency, which is an inherent property of the object. Once the structure and material of a part are determined, the Nth natural frequency can be calculated by CAE simulation, and the variance of the Nth natural frequency can be obtained through common mathematical formulas That's it.

[0043] Therefore, resonance will occur when measuring the stiction force of an electric cooling fan in reality. So, the measured stiction force curve has peaks, while the target stiction force curve does not consider the frequency of the electric cooling fan, and there is a corresponding target stiction force value at each rotational speed.

[0044] For the rotational speed-stiction force value data measured for each electric cooling fan, by using three Gaussian functions to approximate infinitely and combining with the least squares method fitting in Matlab software, the fitting formula ① of the measured stiction force curve can be obtained:[[]]

[0045]

[0046] Among them, a 1 is the maximum allowable unbalance of the electric cooling fan, with the unit of g.mm; m 1 is the rotational speed of the first natural frequency, with the unit of r / min; m 2 is the rotational speed of the second natural frequency, with the unit of r / min; m 3 is the rotational speed of the third natural frequency, with the unit of r / min; S 1 is the variance of the rotational speed of the first natural frequency, with the unit of r / min; s 2 is the variance of the rotational speed of the second natural frequency, with the unit of r / min; s 3 is the variance of the rotational speed of the third natural frequency, with the unit of r / min; X is the rotational speed, with the unit of RPM; F c is the calculated value of the stiction force, with the unit of N.

[0047] Determine the maximum allowable unbalance of the electric cooling fan according to the industrialization ability. Use CAE software to analyze the data of 30 electric cooling fans that meet the vehicle vibration and noise requirements, obtain the natural frequencies of the 30 electric cooling fans, and substitute them into the fitting formula ① to verify the effectiveness of the fitting formula ①.

[0048] Such as Figure 2As shown, the solid line is the rotational speed - stalling force curve obtained through actual measurement of an electric cooling fan using a test device. When the high - speed rotational speed of this electric cooling fan is 2700 RPM, the measured stalling force value is 14.7 N. According to industrialization capabilities, the maximum allowable unbalance of this electric cooling fan is not 260 g.mm. Using CAE software analysis, the first - order natural frequency of this electric cooling fan is 17.9 HZ, the rotational speed at the first - order natural frequency is 1074 r / min, the variance of the first - order natural frequency is 317.2 r / min, the second - order natural frequency is 35.5 HZ, the rotational speed at the second - order natural frequency is 2125 r / min, the variance of the second - order natural frequency is 635 r / min, the third - order natural frequency is 46.2 HZ, the rotational speed at the third - order natural frequency is 2774 r / min, and the variance of the third - order natural frequency is 808.2 r / min. Substituting the above values into fitting formula ①, the calculation result of the stalling force measurement value is as follows:

[0049]

[0050] The error between the measured stalling force value and the stalling force measurement value calculated is:

[0051] (14.88 - 14.7) / 14.7 = 0.01224 = 1.224%.

[0052] The tolerance range between the stalling force measurement value calculated by the fitting formula and the measured stalling force value ≤ ±5%.

[0053] For different rotational speeds and different fans, the above - mentioned calculation process is used to verify the effectiveness of fitting formula ①, which will not be elaborated here. Through verification, it is proved that fitting formula ① is indeed effective. Thus, the above - mentioned fitting formula ① can be used as the stalling force measurement formula, that is, the stalling force measurement formula ② is:

[0054]

[0055] where a 1 is the maximum allowable unbalance of the electric cooling fan, with the unit of g.mm; m 1 is the rotational speed at the first - order natural frequency, with the unit of r / min; m 2 is the rotational speed at the second - order natural frequency, with the unit of r / min; m 3 is the rotational speed at the third - order natural frequency, with the unit of r / min; S 1 is the variance of the rotational speed at the first - order natural frequency, with the unit of r / min; S 2 is the variance of the rotational speed at the second - order natural frequency, with the unit of r / min; S 3 is the variance of the rotational speed at the third - order natural frequency, with the unit of r / min; X is the rotational speed, with the unit of RPM; F c is the stalling force measurement value, with the unit of N.

[0056] For the designed electric cooling fan, the maximum allowable unbalance is determined according to the industrialization capacity, and its natural frequency can be obtained by using CAE software, obtaining its first-order natural frequency and its variance, second-order natural frequency and its variance, and third-order natural frequency and its variance. The measured values of the sticking force of the designed electric cooling fan at different rotational speeds are calculated through the sticking force calculation formula ②, and the rotational speed-sticking force measured value curve is made.

[0057] The rotational speed-sticking force measured value curve is compared with the sticking force target curve: If the measured value of the sticking force is less than or equal to the target value of the sticking force, the designed electric cooling fan meets the vehicle vibration and noise requirements; if the measured value of the sticking force is greater than the target value of the sticking force, the designed electric cooling fan does not meet the vehicle vibration and noise requirements. For the electric cooling fan that does not meet the vehicle vibration and noise requirements, by increasing the height of the fan shroud support to change the stiffness and change the natural frequency of the fan, the sticking force value can be improved to meet the vehicle vibration and noise requirements.

[0058] According to Figure 2 the rotational speed-sticking force curve obtained from the actual measurement of the electric cooling fan shown by the solid line, it can be known that the electric cooling fan does not meet the vehicle vibration and noise requirements in some rotational speed ranges, and this conclusion does not need to be discovered after the electric cooling fan is manufactured. It can be known by calculating the sticking force of the electric cooling fan through the sticking force calculation formula ②, and it can be discovered at the design stage of the electric cooling fan.

[0059] According to the above measurement results, it can be known that when the high-speed rotational speed of the electric cooling fan is 2700 RPM, the measured value of the sticking force Fc is 14.88 N, and the target value of the sticking force F m is:

[0060] F m =(0.00433*X - 3.47) N = 0.00433*2700 - 3.47 = 8.221 N,

[0061] Thus, Fc > F m , and when the high-speed rotational speed of the electric cooling fan is 2700 RPM, the measured value of its sticking force does not meet the vehicle vibration and noise requirements.

[0062] For the electric cooling fan, the calculation formula of its natural frequency f n is as follows:

[0063]

[0064] where K is the stiffness of the electric cooling fan and M is the mass of the electric cooling fan.

[0065] To improve the stalling force of the electric cooling fan to meet the vehicle's vibration and noise requirements, it is necessary to change the natural frequency of the electric cooling fan. Usually, the mass requirement of the electric cooling fan is within a certain range. From the above calculation formula of the natural frequency, it can be seen that changing the stiffness of the electric cooling fan is an effective means to change the natural frequency of the electric cooling fan.

[0066] Therefore, to improve the stalling force of the electric cooling fan to meet the vehicle's vibration and noise requirements, the effective improvement method is: to increase the stiffness of the electric cooling fan and increase the natural frequency of the electric cooling fan.

[0067] Specifically, increasing the height of the air guide ring bracket of the electric cooling fan, increasing the number of air guide ring brackets of the electric cooling fan, and changing the shape of the air guide ring bracket of the electric cooling fan can all increase the stiffness of the electric cooling fan and increase the natural frequency of the electric cooling fan. Among these, increasing the height of the air guide ring bracket of the electric cooling fan, that is, raising the ribs on the surface of the air guide ring bracket, is the simplest and most effective improvement method.

[0068] In this embodiment, by increasing the height of the air guide ring bracket of the electric cooling fan and raising the ribs on the surface of the air guide ring bracket, the stiffness of the electric cooling fan is increased and the natural frequency of the electric cooling fan is increased. Analyzed by CAE software, the first natural frequency of the improved electric cooling fan is 25HZ, the rotational speed of the first natural frequency is 1500r / min, the variance of the first natural frequency is 447.2r / min, the second natural frequency is 55.8HZ, the rotational speed of the second natural frequency is 3350r / min, the variance of the second natural frequency is 981.4r / min, the third natural frequency is 76.7HZ, the rotational speed of the third natural frequency is 4600r / min, the variance of the third natural frequency is 1342.3r / min, and the maximum allowable unbalance is not 260g.mm. Substituting the above values into the stalling force measurement formula ②, the calculation results of the stalling force measurement value after improvement are as follows:

[0069]

[0070] Therefore, Fc′ < F m , when the rotational speed of the improved electric cooling fan is 2700RPM at high speed, the measured value of its stalling force meets the vehicle's vibration and noise requirements. Calculate the measured values of the stalling force of the improved electric cooling fan at different rotational speeds through the stalling force measurement formula ②, and make a stalling force measurement curve of rotational speed - stalling force measurement value, as shown by the solid line in Figure 3 . In the rotational speed range of 1000 - 2700RPM of the improved electric cooling fan, the measured values of its stalling force all meet the vehicle's vibration and noise requirements.

[0071] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings and specific embodiments. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for measuring and evaluating the vibration and noise of an electric cooling fan, characterized in that, it includes the following steps: Step 1: Obtain the rotational speed-stiction force value data of the electric cooling fan; Step 2: Fit the rotational speed-stiction force value data of the electric cooling fan to obtain a stiction force target formula and a stiction force measurement formula: Fit the rotational speed-stiction force value data of multiple electric cooling fans to obtain a stiction force target formula: When the rotational speed of the electric cooling fan is less than or equal to a specific rotational speed, its stiction force target value is a constant value. When the rotational speed of the electric cooling fan is greater than the specific rotational speed, its stiction force target value increases linearly with the rotational speed; Fit the rotational speed-stiction force value data of each electric cooling fan, use the Gaussian function probability density function to obtain a fitting formula, and verify the effectiveness of the fitting formula through the parameters of the electric cooling fan until the effectiveness meets the requirements to obtain the stiction force measurement formula; Step 3: Calculate the stiction force measurement values of the designed electric cooling fan at different rotational speeds through the stiction force measurement formula; Step 4: Generate a stiction force measurement curve based on the rotational speed-stiction force measurement values, generate a stiction force target curve based on the stiction force target formula, and compare the stiction force measurement curve with the stiction force target curve: If the stiction force measurement value is less than or equal to the stiction force target value, the designed electric cooling fan meets the vehicle vibration and noise requirements; If the stiction force measurement value is greater than the stiction force target value, the designed electric cooling fan does not meet the vehicle vibration and noise requirements.

2. The method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 1, characterized in that: In the said Step 1, select multiple electric cooling fans that can meet the vehicle vibration and noise requirements within the used rotational speed range, install the electric cooling fans on a rigid bench through multiple installation and fixing points on the air shroud, install force sensors at the installation positions of multiple installation and fixing points on the bench, connect the force sensors to a charge amplifier, connect the rotational speed sensor of the electric cooling fan to a rotational speed signal converter, connect both the charge amplifier and the rotational speed signal converter to a computer, and measure the stiction force value of the electric cooling fan under different rotational speed conditions.

3. The method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 2, characterized in that: Under different rotational speed conditions, measure the vibration forces in the X, Y, and Z directions at the installation and fixing points of each electric cooling fan through the force sensors, and calculate the stiction force value of the electric cooling fan according to the vibration forces in the X, Y, and Z directions at the installation and fixing points of each electric cooling fan.

4. The method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 1, characterized in that: The said stiction force target formula is obtained through matlab software combined with the least squares method: 0 < X ≤ 1200 RPM, Fm = a N, X > 1200 RPM, Fm = (b * X - c) N, where X is the rotational speed, Fm is the stiction force target value, and a, b, and c are all constants.

5. The method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 4, characterized in that: The fitting formula is obtained by using three Gaussian functions for infinite approximation and combining with the least square method in Matlab software: where, a1 is the maximum allowable unbalance of the electric cooling fan, in g.mm; m1 is the rotational speed of the first-order natural frequency, in r / min; m2 is the rotational speed of the second-order natural frequency, in r / min; m3 is the rotational speed of the third-order natural frequency, in r / min; s1 is the variance of the rotational speed of the first-order natural frequency, in r / min; s2 is the variance of the rotational speed of the second-order natural frequency, in r / min; s3 is the variance of the rotational speed of the third-order natural frequency, in r / min; X is the rotational speed, in RPM; Fc is the measured value of the jamming force, in N; And the validity of the fitting formula is verified by the parameters of the electric cooling fan until the validity meets the requirements, and the formula for calculating the jamming force is obtained.

6. A method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 5, characterized in that: In the validity verification, the maximum allowable unbalance of the measured electric cooling fan is determined according to the industrialization capacity, and the data of the measured electric cooling fan are analyzed by CAE software to obtain the natural frequencies and their variances of each order of the electric cooling fan, and they are substituted into the fitting formula to calculate the measured value of the jamming force. The validity of the fitting formula is verified by comparing the measured value of the jamming force with the calculated value of the jamming force under the same rotational speed condition of the measured electric cooling fan.

7. A method for measuring and evaluating the vibration and noise of an electric cooling fan according to claim 6, characterized in that: In the validity verification, for the measured electric cooling fan, under the same rotational speed condition, the tolerance range between the calculated value of the jamming force by the fitting formula and the measured value of the jamming force ≤ ±5%, then the validity of the fitting formula meets the requirements.

8. A method for measuring and evaluating the vibration and noise of an electric cooling fan according to any one of claims 4-7, characterized in that: It further includes: Step Five: If the designed electric cooling fan does not meet the vehicle vibration and noise requirements, by increasing the stiffness of the electric cooling fan and increasing the natural frequency of the electric cooling fan, the changed maximum allowable unbalance and the natural frequencies and their variances of each order are obtained; Step Six: Repeat Steps Three to Five until the changed electric cooling fan meets the vehicle vibration and noise requirements.

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