A test method for high-frequency dynamic characteristics of a rubber mount for an electric vehicle

Abstract

The present invention relates to a high-frequency dynamic characteristic test method for a rubber mount of an electric vehicle, belonging to the technical field of vehicle mount tests. It can find out the main influencing factors of high-frequency dynamic characteristics by analyzing the boundary conditions of the mount dynamic characteristic test, identify the corresponding relationship and influence law between the dynamic characteristics and the main factors, so as to expand the guiding principles for the design and optimization of electric vehicle mounts and their brackets. The method includes: S1, designing a fixture for fixing the rubber mount; S2, taking the mount stiffness, the fixture mode, and the rubber mount mode as single variables respectively, and conducting high-frequency dynamic characteristic tests respectively to obtain the influence law of each variable on the vibration peak value in three frequency bands of 1000 Hz - 1200 Hz, 1500 Hz - 1650 Hz, and 1900 Hz - 2300 Hz.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive mount tests, and particularly to a high-frequency dynamic characteristic test method for rubber mounts of electric vehicles. Background Art

[0002] At present, reducing the consumption of fossil energy has become an international trend. Under this trend, clean energy such as wind, light, and water, as well as battery energy storage technologies, have developed rapidly. New energy vehicles have entered people's lives due to their environmental friendliness and have quickly become the focus of research and development in the automotive industry.

[0003] Compared with hybrid vehicles, electric vehicles do not require the design and development of very complex control strategies, and their architectures and structures are relatively simple, becoming the product trend of new energy vehicles. The NVH performance of electric vehicles is the most significant vehicle dynamic quality perceived by passengers. Its power is different from that of traditional fuel vehicles. Due to the lack of the masking effect of the engine, although the noise level is decreasing, the significant increase in the noise frequency makes passengers more likely to perceive the change in the overall vehicle sound quality, posing higher requirements for the development and control of NVH high-frequency performance.

[0004] The highest frequency of the commonly used electro-hydraulic servo mount dynamic characteristic test equipment is only 500 Hz. The test of the higher frequency dynamic characteristics of rubber mounts is limited by the equipment and lacks research, resulting in less understanding of the high-frequency dynamic characteristics of rubber mounts.

[0005] Therefore, it is necessary to study a high-frequency dynamic characteristic test method for rubber mounts of electric vehicles to address the deficiencies of the existing technology and solve or mitigate one or more of the above problems. Summary of the Invention

[0006] In view of this, the present invention provides a high-frequency dynamic characteristic test method for rubber mounts of electric vehicles, which can find out the main influencing factors of high-frequency dynamic characteristics by analyzing the boundary conditions of the mount dynamic characteristic test, identify the corresponding relationship and influence law between the dynamic characteristics and the main factors, so as to expand the guiding principles for the design and optimization of electric vehicle mounts and their brackets.

[0007] On the one hand, the present invention provides a high-frequency dynamic characteristic test method for rubber mounts of electric vehicles, and the method includes:

[0008] S1. Design a fixture for fixing the rubber mount;

[0009] S2. Respectively take the mount stiffness, the fixture mode, and the rubber mount mode as single variables, and respectively conduct high-frequency dynamic characteristic tests to obtain the influence law of each variable on the vibration peak value in three frequency bands of 1000 Hz - 1200 Hz, 1500 Hz - 1650 Hz, and 1900 Hz - 2300 Hz.

[0010] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where the suspension stiffness is 800 N / mm, 630 N / mm, or 475 N / mm. When the suspension stiffness is the single variable, its value is selected in descending order from 800 N / mm, 630 N / mm, and 475 N / mm, and high-frequency dynamic characteristic tests are respectively carried out; when the fixture mode or the rubber suspension mode is the single variable, the suspension stiffness is selected as any one of 800 N / mm, 630 N / mm, and 475 N / mm and remains unchanged.

[0011] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where the fixture includes an upper fixture and a lower fixture; the active end bracket of the rubber suspension is fixed on the upper fixture, and the passive end bracket of the rubber suspension is fixed on the lower fixture; the upper fixture and the lower fixture are respectively fixedly connected to two test ends of the m+p electromagnetic high-frequency test equipment;

[0012] The material of the upper fixture is aviation aluminum, and the weight is 2.248 Kg;

[0013] The material of the lower fixture is aviation aluminum, and the weight is 2.272 Kg.

[0014] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where the upper fixture includes a square plate member at the upper end and two left and right ear forks fixedly arranged below the square plate member, and first specimen fixing holes are provided at the lower ends of the two ear forks; the active end bracket of the rubber suspension is fixed in the middle of the two ear forks by bolts.

[0015] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where the lower fixture includes a circular plate member at the lower end and a semi-conical frustum fixedly arranged on the circular plate member, a groove with openings on both the upper and side surfaces is provided on the side wall of the semi-conical frustum, and a number of second specimen fixing holes are provided on the side wall of the groove; the passive end bracket of the rubber suspension is fixed on the second specimen fixing holes by bolts.

[0016] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where taking the fixture mode as the single variable specifically means: successively attaching weights of different weights to the upper fixture or the lower fixture.

[0017] For the aspects and any possible implementation manners described above, a further implementation manner is provided, where taking the fixture mode as the single variable specifically means: successively attaching weights of different weights to the sides of the ear forks.

[0018] For the aspects and any possible implementation manners described above, a further implementation manner is provided. Specifically, taking the rubber mount mode as a single variable, different weights of heavy objects are sequentially added to the circular tube housing of the passive end bracket of the rubber mount.

[0019] For the aspects and any possible implementation manners described above, a further implementation manner is provided. Specifically, the heavy objects with different weights are heavy objects with weights of 0g, 45g, and 90g.

[0020] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The ear fork has a symmetrical structure that is wider at the top and narrower at the bottom with two inclined surfaces on the left and right. The slope of the inclined surface is 18 degrees. The inclined surface is the side of the aforementioned ear fork for attaching different heavy objects.

[0021] Compared with the prior art, one of the technical solutions in the above technical solutions has the following advantages or beneficial effects: Based on the upgrading of the equipment, the upper frequency limit of the dynamic characteristic test of the rubber mount is significantly increased from the traditional 500Hz to 3000Hz. And in order to reduce the influence of the fixture mode on the dynamic characteristic test of the mount, a fixture design reference is proposed.

[0022] Another technical solution in the above technical solutions has the following advantages or beneficial effects: Based on the dynamic characteristic test results, the main influencing factors of the three peaks of the high-frequency dynamic stiffness are explored, and a method for identification is proposed through the schemes of different stiffnesses and different additional masses, and then conclusions are drawn.

[0023] Another technical solution in the above technical solutions has the following advantages or beneficial effects: Based on the dynamic characteristic test results and combined with the modal analysis of the test boundary conditions, the guiding principles for the design and optimization of the electric vehicle mount and its bracket are obtained: The changes in the mount stiffness and the passive end mass have obvious effects on the high-frequency dynamic characteristics of the mount. Reducing the initial stiffness of the mount or adding mass to the passive end bracket can effectively reduce the peak value of the mount dynamic stiffness, and further reduce the structural noise transmission.

[0024] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned technical effects simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 It is a structural diagram of the right rear bushing type rubber mount assembly of the front electric drive assembly provided by an embodiment of the present invention.

[0027] Figure 2 This is a physical diagram of the m + p suspension high-frequency dynamic characteristic test bench provided by an embodiment of the present invention;

[0028] Figure 3 This is an assembly of a suspension sample and a fixture provided by an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the modal analysis results of a suspension high-frequency test fixture provided by an embodiment of the present invention; among them, (a) is the first-order diagram, (b) is the second-order diagram, and (c) is the third-order diagram;

[0030] Figure 5 This is a curve graph of the test results of the suspension dynamic characteristics provided by an embodiment of the present invention;

[0031] Figure 6 This is a schematic diagram of the additional mass position provided by an embodiment of the present invention;

[0032] Figure 7 This is a curve graph of the test results of the dynamic characteristics of suspensions with different initial stiffnesses provided by an embodiment of the present invention;

[0033] Figure 8 This is a curve graph of the test results of the dynamic characteristics of different additional masses on the passive end bracket provided by an embodiment of the present invention;

[0034] Figure 9 This is a curve graph of the test results of the dynamic characteristics of different additional masses on the upper fixture provided by an embodiment of the present invention. Detailed implementation manners

[0035] For a better understanding of the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] The object of the present invention can be achieved through the following technical solutions:

[0038] Test object: All four suspensions of the front electric drive assembly and its suspension system are bushing-type rubber suspensions. In the present invention, the right rear suspension is taken as the object of high-frequency test research, and its structure is as Figure 1As shown in the figure. The structure of the right rear mount includes an active end bracket and a passive end bracket. The active end bracket (i.e., the mount bracket) is in the shape of a horizontally lying cylinder as a whole, and includes a core shaft inside, a rubber main spring provided on the outer periphery of the core shaft, and an aluminum alloy outer tube provided on the outer periphery of the rubber main spring. The core shaft has a hollow structure for bolts to pass through to realize the suspension and fixation of the entire mount sample. The passive end bracket is provided below the mount bracket and is in the shape of a groove as a whole. The cross-section of the groove opening of the groove is square, and the side surface is in the shape of a quasi-triangle. The difference between this quasi-triangle and a general triangle is that one side at the connection with the cylindrical active end bracket is arc-shaped. Four threaded holes are provided on the passive end bracket for fixing with the test equipment, and the setting direction of the threaded holes is perpendicular to the axial plane of the active end bracket.

[0039] Test equipment: A new type of m+p electromagnetic high-frequency test equipment is used in the test. Its test frequency range is 50 - 3000 Hz, and the maximum preload is 5000 N. The mount dynamic characteristic test bench is as Figure 2 shown.

[0040] Fixture design: The highest test frequency is 3000 Hz. Due to the clamping form, it is not easy for the fixture mode to be much higher than the test frequency. To reduce the influence of the fixture mode on the mount dynamic characteristic test, it is necessary to try to increase the first-order mode frequency of the fixture. 7075 aviation aluminum alloy material with light weight, high specific stiffness and good formability is selected for the design and manufacture of the fixture. The assembly of the mount sample and the fixture is as Figure 3 shown. The fixture is designed for the test object and test equipment as Figure 3As shown in the figure. The fixture includes an upper fixture and a lower fixture (the materials of the upper and lower fixtures are aviation aluminum), and the suspension sample is arranged between the upper and lower fixtures. The upper end of the upper fixture is a square thick plate structure, and a fork-shaped structure (ear fork) is arranged below the square thick plate structure, that is, downward-facing ear forks for fixing the active end of the suspension are respectively fixed at both ends of the square thick plate structure, and the two ear forks are arranged parallel and opposite to each other; the ear forks and the square thick plate are preferably integrally formed to ensure the connection strength between the two; first sample fixing holes are arranged at the lower ends of both ear forks, and the active end of the suspension sample is fixed on the upper fixture through bolts and nuts. The thickness of the square thick plate of the upper fixture is 0.029 m. The ear forks are wider at the top and narrower at the bottom with two left and right inclined surfaces, and the slope of the two inclined surfaces of the ear fork is 18 degrees. The overall weight of the upper fixture is 2.248 Kg. The lower end of the lower fixture is a circular thick plate structure, and a semi-cone frustum structure is arranged on the circular thick plate structure. The semi-cone frustum structure is a structure that is cut off nearly half along the axial direction of the cone frustum (the arc occupied by the cone frustum is 214 degrees), and a groove is arranged at the cut surface for the quasi-square structure at the bottom of the suspension sample to be placed in. There are four second sample fixing holes on the groove wall, and the quasi-square structure at the bottom of the suspension sample is fixed in the groove of the lower fixture through bolts and nuts. The weight of the lower fixture is 2.272 Kg. A number of fixture fixing holes are arranged on the square thick plate structure of the upper fixture and the circular thick plate structure of the lower fixture, and they are respectively fixedly connected to the upper test end and the lower test end of the m+p electromagnetic high-frequency test equipment through bolts and nuts to conduct high-frequency dynamic characteristic tests.

[0041] To explore the influence of the fixture mode, modal analysis of the fixture is carried out. During the analysis, the upper and lower fixtures and the mounting bolts are retained, and the suspension and its passive end bracket are simplified into a linear spring and an equivalent mass. The analysis results are as Figure 4 shown. There are three-order fixture modes within 3000 Hz. The first-order mode is mainly the Z-direction mode, that is, the position of the suspension core shaft and the bolts used to connect the core shaft and the upper fixture; the second-order mode is mainly the X-direction swing, that is, the ear fork part of the upper fixture, and the point with the largest displacement is near the connection point between the bolt and the fixture, that is, the end of the ear fork; the third-order mode is mainly the Y-direction swing of the lower fixture. The above three-order modes will be reflected in the test results of the dynamic characteristics of the rubber suspension at 3000 Hz.

[0042] In the case where it is impossible to avoid the influence of the fixture mode on the high-frequency dynamic characteristics, there are three main influencing factors for the high-frequency dynamic characteristics of the suspension: suspension stiffness, fixture mode, and suspension bracket mode (the suspension bracket is the upper half of the suspension sample, the active end bracket). The above factors interact with each other and jointly affect the test results of the suspension dynamic characteristics.

[0043] Test plan: Based on the above test equipment and clamping system, design a test plan, assemble the suspension sample and the fixture and install them on the high-frequency test equipment, as Figure 2As shown, apply a preload of 350 N in the Z direction at the upper end, with the lower end as the actuator end, and apply an equal-amplitude acceleration excitation of ±3g with a sweep rate of 2 Oct / min. Measure the force signal at the upper end and calculate the dynamic stiffness at the suspension cross-point accordingly. The results are as Figure 5 shown.

[0044] To explore the main influencing factors of the three peaks of the high-frequency dynamic stiffness (as Figure 5 shown), different stiffness and additional mass schemes will be used for identification. Control a single variable, conduct experiments one by one, and then compare and study. The experimental schemes and purposes are shown in Table 1. The initial dynamic stiffnesses of the three suspension samples at 50 Hz are 800, 630, and 475 N / mm respectively, decreasing in sequence, and numbered 1#, 2#, and 3#.

[0045] Table 1 Experimental research schemes and purposes for influencing factors of suspension high-frequency dynamic characteristics

[0046]

[0047] First, change the stiffness of the suspension samples by adjusting the rubber hardness and conduct high-frequency dynamic characteristic tests. The initial dynamic stiffnesses of the three suspension samples at 50 Hz are 800 N / mm, 630 N / mm, and 475 N / mm respectively, decreasing in sequence, and numbered 1#, 2#, and 3#. With other test conditions unchanged, the test results are as Figure 7 shown. The results show that the suspension stiffness has a greater impact on the dynamic characteristics in the entire frequency band. As the initial stiffness decreases, the dynamic stiffness in the entire frequency band decreases; especially the peak value and its frequency near 1200 Hz (the vibration peak value in the 1000 Hz - 1200 Hz frequency band) gradually decrease, indicating that the peak frequency is positively correlated with the suspension stiffness; the peak value at 1500 Hz (the vibration peak value in the 1500 Hz - 1650 Hz frequency band) remains basically unchanged; the peak value at 2000 Hz (the vibration peak value in the 1900 Hz - 2300 Hz frequency band) has no obvious gradient law with the change of stiffness.

[0048] Second, for the 1# and 2# suspension samples, attach additional masses of 0 g (i.e., no additional mass), 45 g, and 90 g respectively to the outer shell of the circular tube of the passive end bracket of the suspension. With other test conditions unchanged, the measured dynamic stiffness results are as Figure 8As shown, where (a) is the test result of the 1# suspension sample and (b) is the test result of the 2# suspension sample. The results show that adding additional mass to the passive end bracket has no effect on the peaks at 1200 Hz and 1500 Hz; however, with the increase of additional mass, the peak value of dynamic stiffness near 2000 Hz and its frequency gradually decrease, and the gradient law is more significant. The positions of the additional masses of the 1# sample and the 2# sample are slightly different. The additional mass of the 2# sample is in the middle of the bracket circular tube structure, and the additional mass of the 1# sample is in the upper part of the circular tube structure. The change trend of the peak value of dynamic stiffness and frequency near 2000 Hz of the 2# sample is more obvious, indicating that the dynamic characteristics are sensitive to the position of the additional mass at the passive end.

[0049] Third, based on the high-frequency dynamic characteristic test of the 1# sample without any additional mass, a total of 90 g of mass was added to both sides with the largest modal displacement of the upper fixture, and the other test conditions remained unchanged. The test results of the dynamic characteristics are as Figure 9 . The results show that adding mass to the upper fixture has little effect on the dynamic characteristics in the whole frequency band, and only the peak value at 1500 Hz and its frequency decrease slightly. In fact, the test results of this scheme for the 2# and 3# samples are all like this, and the consistency is very good.

[0050] Based on the test results of the dynamic characteristics and combined with the modal analysis of the test boundary conditions, the influence laws of various factors on the dynamic characteristics are summarized in Table 2.

[0051] Table 2 Influence laws of various factors on the dynamic characteristics of the suspension

[0052]

[0053]

[0054] The engineering application of the above conclusions on the whole vehicle is analyzed as follows because the boundary conditions change.

[0055] 1200 Hz peak: In the dynamic characteristic test, adding mass to the upper fixture and the passive end bracket of the suspension has no effect on it, while reducing the suspension stiffness, this peak value and its frequency decrease significantly; combined with the simulation analysis results, it is judged that it is caused by the Z-direction mode of the mandrel and its bolts. In the whole vehicle state, this mode will correspond to the mode of the active end bracket of the suspension. The test shows that the mode frequency of the active end bracket is positively correlated with the initial stiffness of the suspension. Therefore, to improve the vibration isolation and noise reduction ability of the suspension in the whole frequency band, it is necessary to reduce the initial stiffness of the suspension within a reasonable range. The excitation frequency of electric vehicles is relatively high (for example, the order frequency of the main reducer can reach 1000 Hz). To avoid the deterioration of structural noise, it is necessary to further improve the mode of the active end bracket.

[0056] 1500 Hz peak: The initial stiffness change of the mount and the additional mass of the passive end bracket have no effect on this peak. Only after adding the additional mass to the upper fixture, the peak value and frequency decrease slightly. This peak is caused by the X-direction mode of the upper fixture. However, in the dynamic characteristic test, the excitation direction is nearly orthogonal to the X-direction mode of the upper fixture, and the radial dynamic characteristics are less affected by the axial structural mode. In the vehicle state, the constraint of the active end of the mount is generally weaker than that of the test upper fixture, and the modes are not necessarily orthogonal, which may cause corresponding structural noise.

[0057] 2000 Hz peak: The peak value and its frequency are negatively correlated with the additional mass of the passive end bracket, and the gradient law is obvious. It is judged that this peak is caused by the mode of the round head part of the passive end bracket. According to the significant inhibitory effect of the additional mass on the dynamic characteristics, mass can be added at the vibration peak of the passive end of the mount to reduce the transmission of the peak vibration. In the vehicle state, the body structure connected to the passive end bracket is weaker in stiffness than the test lower fixture, and its modal frequency may be lower than 2000 Hz.

[0058] Furthermore, the guiding principles for the design and optimization of the electric vehicle mount and its bracket are obtained: The changes in the mount stiffness and the mass of the passive end have obvious effects on the high-frequency dynamic characteristics of the mount. Reducing the initial stiffness of the mount or adding mass to the passive end bracket can effectively reduce the peak value of the dynamic stiffness of the mount, and thus reduce the transmission of structural noise.

[0059] In this invention, an M+P high-frequency test bench needs to be selected for the test equipment. In the fixture design, to reduce the influence of the fixture mode on the dynamic characteristic test of the mount, it is necessary to improve the fixture strength and reduce the fixture weight to increase the first-order modal frequency of the fixture as much as possible. The 7075 aviation aluminum alloy material with light weight, high specific stiffness and good formability is selected for the fixture design and manufacture.

[0060] The above has introduced in detail a method for testing the high-frequency dynamic characteristics of an electric vehicle rubber mount provided by an embodiment of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount, characterized in that, the method comprises: S1. Design a fixture for fixing the rubber mount; wherein, the fixture includes an upper fixture and a lower fixture; the active end bracket of the rubber mount is fixed on the upper fixture, and the passive end bracket of the rubber mount is fixed on the lower fixture; the upper fixture and the lower fixture are respectively fixedly connected to two test ends of an m+p electromagnetic high-frequency test device; the upper fixture includes a square plate member at the upper end and two left and right ear forks fixed below the square plate member, and first specimen fixing holes are provided at the lower ends of the two ear forks; the active end bracket of the rubber mount is fixed in the middle of the two ear forks by bolts; the lower fixture includes a circular plate member at the lower end and a semi-conical frustum fixed on the circular plate member, a groove with openings on both the upper and side surfaces is provided on the side wall of the semi-conical frustum, and a plurality of second specimen fixing holes are provided on the side wall of the groove; the passive end bracket of the rubber mount is fixed on the second specimen fixing holes by bolts; S2. Respectively taking the mount stiffness, the fixture mode, and the rubber mount mode as single variables, conduct high-frequency dynamic characteristic tests to obtain the influence rules of each variable on the vibration peak values in three frequency bands of 1000 Hz - 1200 Hz, 1500 Hz - 1650 Hz, and 1900 Hz - 2300 Hz; wherein, taking the fixture mode as a single variable specifically means: successively attaching weights of different weights on the upper fixture or the lower fixture; taking the rubber mount mode as a single variable specifically means: successively attaching weights of different weights on the circular tube shell of the passive end bracket of the rubber mount.

2. The test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount according to claim 1, characterized in that, the mount stiffness is 800 N / mm, 630 N / mm, or 475 N / mm.

3. The test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount according to claim 1, characterized in that, the materials of the upper fixture and the lower fixture are both aviation aluminum, the weight of the upper fixture is 2.248 Kg; the weight of the lower fixture is 2.272 Kg.

4. The test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount according to claim 1, characterized in that, taking the fixture mode as a single variable specifically means: successively attaching weights of different weights on the side of the ear fork.

5. The test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount according to any one of claim 4, characterized in that, the weights of different weights are specifically weights of 0 g, 45 g, and 90 g.

6. The test method for the high-frequency dynamic characteristics of an electric vehicle rubber mount according to claim 1, characterized in that, the ear fork is a symmetric structure with a wider upper part and a narrower lower part and having two left and right inclined surfaces, and the slope of the inclined surface is 18 degrees.

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