Method for determining bolt loosening of a cantilever structure of a passenger car body

Abstract

The present application relates to a kind of passenger car body cantilever structure piece bolt looseness determination method;Including the analysis of body connection point load spectrum based on road spectrum, the analysis of cantilever structure piece fastening bolt loading time history based on body connection point load spectrum, the bolt movement determination based on cantilever structure piece fastening bolt loading time history, all road bolt movement frequency statistics, comprehensive analysis is given a quantitative index for evaluating bolt movement;Through the method of the present application, structure improvement or bolt performance improvement, calculate the statistics of all road bolt movement frequency again and compare with original index, examine improvement effect, by calculating and determining bolt movement frequency in cantilever structure piece part design stage, to judge the risk of cantilever structure piece bolt looseness, and propose effective improvement measures, avoid bolt looseness failure problem of later body cantilever structure piece fastening bolt and change, shorten development cycle, reduce research and development cost, improve product design quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of CAE simulation technology in automobile development, and particularly relates to a method for judging bolt loosening of a cantilever structure of a passenger car body. BACKGROUND

[0002] Many installation structures are attached to the car body, including: battery, DCDC, electronic and electrical equipment, etc. Many structures need to be connected with the car body, and inevitably become suspended (cantilevered) structures after connection. Such structure forms are prone to cause resonance phenomenon, not only causing great damage to the structure, but also easily leading to failure of bolt connection, causing bolt loosening, and even breaking. In the process of reliability test or post-test inspection, it is often found that the fastening bolts of such structures are loose. If the problem is found in the product development process at this stage, the improvement space is small, the difficulty is great, the cost is high, and the product development cycle is seriously delayed.

[0003] The traditional method only selects the fastener in the product design stage by experience, and the load input for checking is the theoretical calculation under ideal state, which cannot meet the accuracy of complex engineering actual structure, cannot reflect the detailed position of complex structure, cannot perform quantitative evaluation of bolt loosening, and cannot verify the effect of structure improvement.

[0004] In recent years, with the shortening of the development cycle of passenger cars, severe challenges are put forward to each link of development, and each professional needs to intervene in advance to ensure product quality by using advanced technical means. It is particularly important to evaluate performance at the project platform vehicle stage. The evaluation of the loosening risk of the structure fastening bolt of the cantilever structure at the initial stage of the car body structure design based on the actual load is of great help to shorten the development cycle, improve the accuracy of risk identification, and improve the development efficiency.

[0005] The prior art discloses a bolt loosening life prediction method, which monitors the bolt loosening degree under different displacement amplitude levels, collects the residual pre-tightening force data of each stage under each displacement amplitude, refers to the material S N curve in fatigue research, and draws the initial pre-tightening force residual percentage and vibration displacement amplitude life (D N) curve under different loosening conditions. Through the bolt loosening cumulative mechanism, a bolt loosening linear cumulative model is established. The D N curve and expression of a specific bolt are measured through an experiment, and the bolt loosening life is predicted by using the displacement amplitude loosening life (D N) curve and the bolt loosening linear cumulative model. The prediction method is to monitor the pre-tightening force under different amplitude levels, and draw the vibration displacement amplitude life (D N) curve. The prior art also discloses a bolt loosening monitoring device and a bolt loosening monitoring method. A first end portion of a magnetic gasket is provided with a bolt hole, the first end portion is sleeved on a screw rod through the bolt hole, the first end portion is clamped between a bolt head of the bolt and a to-be-connected component, and the magnetic gasket and the bolt have a circumferential synchronous displacement, or the first end portion is clamped between a nut and the to-be-connected component, and the magnetic gasket and the nut have a circumferential synchronous displacement; a second end portion of the magnetic gasket extends out of the bolt head or the nut, the second end portion is provided with a steel wire hole for sleeving the steel wire, and a tail end of the steel wire is fixedly connected with the signal emitting device. When the bolt loosens, the bolt or the nut drives the magnetic gasket to move synchronously in the circumferential direction, and pulls the steel wire. The steel wire triggers the signal emitting device to send a bolt loosening signal. The monitoring method tests the bolt loosening by using a specific device.

[0006] The prior art also discloses a locomotive bogie bolt loosening fault detection method. A locomotive bogie bolt loosening fault detection test platform is composed of a signal generating device, a power output device, a detection piece, a signal collecting device, a signal analyzing device and a bolt disassembling device. The platform is built to obtain the state characteristic information of the locomotive bogie bolt loosening by using an acceleration sensor, extract the sensitive characteristic quantity of the locomotive bogie bolt loosening state by using a time-frequency characteristic extraction technology, modalize the sensitive characteristic quantity by using a modal interval error analysis method, and recognize the locomotive bogie bolt loosening state by using a modal interval least square support vector machine pattern recognition method. The detection method collects the acceleration signal, extracts the sensitive characteristic quantity of the locomotive bogie bolt loosening state by using a time-frequency characteristic extraction technology, modalizes the sensitive characteristic quantity by using a modal interval error analysis method, and recognizes the locomotive bogie bolt loosening state by using a modal interval least square support vector machine pattern recognition method.

[0007] However, the above method has the defects of inaccurate load input condition, inability to consider detailed structure connection position, and inability to perform structure improvement checking. SUMMARY

[0008] The purpose of the present application is to provide a passenger car body cantilever structure bolt looseness determination method based on road spectrum and modal transient response analysis simulation to solve the problems of inaccurate load input condition, inability to consider detailed structure connection position, inability to perform structure improvement checking, and inaccurate calculation results in the prior art.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] A passenger car body cantilever structure bolt looseness determination method comprises the following steps:

[0011] A, body connection point load spectrum analysis based on road spectrum;

[0012] B, cantilever structure fastening bolt load time history analysis based on body connection point load spectrum;

[0013] C, bolt looseness determination based on cantilever structure fastening bolt load time history;

[0014] D, all-terrain bolt looseness frequency statistics.

[0015] Further, step A is specifically: based on the test track road spectrum, a whole vehicle multi-body model is built, and the virtual iteration method is used to extract the load spectrum of the body connection point.

[0016] Further, the actual test track four-wheel hub six-component force road spectrum force signal is input, a whole vehicle multi-body dynamics model is built, and the virtual iteration method is used to extract the force / torque signal of all connection points FX, FY, FZ, MX, MY, and MZ of the body-in-white.

[0017] Further, step B is specifically: based on the load spectrum of the body connection point, the cantilever structure is mounted on the all-interior body-in-white model, the connecting bolts between them are rigid springs, modal transient dynamic analysis is performed, and the all-terrain longitudinal and two radial internal force response spectra of the rigid spring are extracted.

[0018] Further, the method comprises the following steps:

[0019] B1, the force / torque signal of all connection points FX, FY, FZ, MX, MY, and MZ of the body-in-white is used as the load input condition;

[0020] B2, with the full interior white body grid model, the cantilever structure assembly grid model to be evaluated is carried, and the bolt connection between the cantilever structure assembly and the white body grid is connected by a rigid spring unit;

[0021] B3, the transient dynamics response analysis based on the modal above grid model free mode is calculated, and the longitudinal and two radial force response time history curve signals of the bolt rigid spring unit are obtained.

[0022] Further, step C, specifically: the rigid spring full road internal force response spectrum sample of each time is subjected to formula determination, such as bolt radial force * friction coefficient < bolt radial internal force, then it is considered that the bolt is moved 1 time, otherwise it is considered that there is no movement.

[0023] Further, the determination basis is that the force value obtained by multiplying the friction coefficient after the bolt pretightening force is reduced by the longitudinal load external force is the critical value of bolt movement, such as the bolt longitudinal load external force is greater than the critical value, then it is considered that the bolt is moved 1 time; otherwise, it is considered that the bolt does not move.

[0024] Further, all sample points in the longitudinal and two radial force response time history curve signals of the bolt rigid spring unit are determined according to the above determination basis, and the corresponding determination number result is obtained.

[0025] Further, step D, specifically: all road samples are statistically analyzed, the sum of the movement times of each different road of the test field is multiplied by the corresponding movement times of all roads, and the sum of the movement times is the final determination result.

[0026] Further, the statistical results are respectively classified and accumulated according to different road types and full test mileage.

[0027] Compared with the prior art, the beneficial effects of the present application are:

[0028] The present application extracts the external load of the bolt unit by using the body CAE technology, and then determines whether the bolt moves and the movement times according to the corresponding criteria; based on the actual road load spectrum, the finite element technology is applied, and the vibration performance of the structure is considered, so that the bolt movement of the detailed structure at different positions can be accurately reflected. And in a certain quantitative form, the trend of the bolt movement of the same structure and different bolts, and the bolt movement trend between different structures are accurately reflected. BRIEF DESCRIPTION OF DRAWINGS

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of the main implementation steps of the present invention;

[0031] Figure 2 Finite element model of the entire interior of the vehicle body, finite element model of the cantilever structural components, and schematic diagram of the bolted rigid connector between the two;

[0032] Figures 3a-3b This invention relates to the input signal and loading schematic diagram for modal dynamic response analysis;

[0033] Figure 4 This is a schematic diagram of the bolt movement determination standard of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments:

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0036] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0037] This invention discloses a method for determining the loosening of bolts in a cantilever structure component of a passenger vehicle body, comprising the following steps:

[0038] 1. Load spectrum analysis of vehicle body connection points based on road spectrum;

[0039] 2. Load time history analysis of fastening bolts of cantilever structural components based on load spectrum of vehicle body connection points;

[0040] 3. Determination of bolt movement based on the loading time history of fastening bolts in cantilever structures;

[0041] 4. Statistics on the number of bolt movement occurrences across the entire road surface.

[0042] The body connection point load spectrum analysis based on the road spectrum comprises: building a whole vehicle multi-body model based on the test track road spectrum, and extracting the load spectrum of the body connection point by using a virtual iteration technique.

[0043] The cantilever structure fastening bolt loading time history analysis based on the body connection point load spectrum comprises: based on the body connection point load spectrum, loading the whole interior white body model on the cantilever structure, using a rigid spring for the connecting bolt therebetween, performing modal transient dynamic analysis, and extracting the whole road surface longitudinal and two radial internal force response spectra of the rigid spring.

[0044] The bolt looseness determination based on the cantilever structure fastening bolt loading time history comprises: performing formula determination on the whole road surface internal force response spectrum sample of the rigid spring at each time, and if bolt radial force * friction coefficient < bolt radial internal force, the bolt is considered to loosen once, otherwise, the bolt is considered not to loosen.

[0045] The whole road surface bolt looseness number statistics comprises: performing statistics on all the time samples of the whole road surface, including the sum of the looseness numbers of each different road of the test track, and the sum of the looseness numbers corresponding to all the road surface and the response circle number (the whole test history according to the test track specification), and the sum is the final result of the method.

[0046] The application compares the results of different structure improvement schemes by the above steps, and views the comparison advantages and disadvantages of the structure or scheme and the improvement effect. After structure improvement or bolt performance optimization selection, the above process is executed again, the calculation results are compared with the original scheme, the improvement effect is viewed, and a basis is provided for design.

[0047] The application overcomes the defects of the prior art, such as inaccurate load input condition, inability to consider detailed structure connection position, inability to perform structure improvement verification, and inaccurate calculation result.

[0048] To achieve the above object, the application can accurately reflect the bolt looseness of different positions of the detailed structure based on the actual road load spectrum, application of the finite element technology and consideration of the vibration performance of the structure. The situation is reflected in a certain quantitative form, and the bolt looseness trend of the same structure and different bolts and different structures is accurately reflected.

[0049] As Figure 1As shown, the present application uses actual test track spectrum to apply multi-body dynamics model and virtual iteration technology to obtain the load spectrum at the body connection point as the input condition for the next step; uses the body connection point load spectrum and combines the full interior body and cantilever structure assembly finite element model to apply modal transient dynamic analysis to obtain the loading time history of the cantilever structure fastening bolt as the input condition for the next step; the bolt loosening judgment based on the cantilever structure fastening bolt loading time history data and the full road bolt loosening frequency statistics are the calculation results of the first analysis; view the results, identify the most dangerous bolt, the road type that has the greatest impact on bolt loosening, and the bolt loosening frequency degree of the full mileage; apply the above process to verify and compare the results of different structure improvement schemes, and view the comparison of the pros and cons of the structure or scheme and the improvement effect.

[0050] Embodiment 1

[0051] The cantilever structure fastening bolt loading time history analysis based on the body connection point load spectrum includes the following contents: taking the actual test track four wheel hub six force spectrum force signals as input, building a whole vehicle multi-body dynamics model, applying virtual iteration technology, extracting the force / torque signals of all connection points FX, FY, FZ, MX, MY, MZ of the body-in-white in six degrees of freedom as the load input condition for the next step.

[0052] The cantilever structure fastening bolt loading time history analysis based on the body connection point load spectrum includes the following contents: taking the force / torque signals of all connection points FX, FY, FZ, MX, MY, MZ of the body-in-white in six degrees of freedom as the load input condition; based on the ABAQUS / strandard software platform, taking the full interior body-in-white grid model, carrying the cantilever structure assembly grid model to be evaluated, the bolt connection between the cantilever structure assembly and the body-in-white grid is connected by rigid spring element, and the bushing connection type in the connector connector is applied, as shown in Figure 2 The transient dynamics response analysis based on the modal grid model free modal is calculated.

[0053] Firstly, the structure modal is extracted by applying the *frequency keyword (the frequency range can be selected as needed), and then the modal transient dynamic response analysis is solved based on the modal results by applying the *modal transient dynamic keyword, and the longitudinal and two radial force response time history curve signals of the bolt connector connector rigid spring element are obtained by applying the CTF card output in the *output keyword, and the resolution of the output signal is greater than that of the load input signal, as the load input condition for the next step, as shown in FIG. 3.

[0054] The bolt loosening determination based on the time history data of the load time history of the fastening bolt of the cantilever structure includes the following: the determination of bolt loosening is defined as: after the bolt pre-tightening force is reduced by the longitudinal load external force, the force value obtained by multiplying the friction coefficient is the critical value of bolt loosening. If the bolt longitudinal load external force is greater than the critical value, it is considered that the bolt loosens once; otherwise, it is considered that the bolt does not loosen, as shown in the following formula. Figure 4 Figure 4 In the formula, F3>(F1-F2)·μ, where F1 is the bolt assembly pre-tightening force, F2 is the bolt axial force caused by the external load, F3 is the bolt radial force caused by the external load, and μ is the friction coefficient between the connected parts.

[0055] All sample points in the longitudinal and two radial force response time history curve signals of each bolt rigid spring unit in the structure are determined according to the above determination basis to obtain the corresponding determination number results.

[0056] The bolt loosening number statistics of the full road surface includes the following: the above statistical results are respectively accumulated according to different road types and full test mileage.

[0057] The different road type accumulation statistical results show that in which specific road type, the bolt loosening trend is most obvious, and according to the frequency characteristics of the road type, the basis for the subsequent improvement direction is provided.

[0058] The full test mileage accumulation statistical results show that in the whole test process, how many times the bolt loosens by using the method as a ruler. Different bolts in the structure are compared to determine which structure position of the bolt has the most obvious loosening trend, that is, which structure position has the most dangerous connection, and the basis for the subsequent improvement direction is provided. The stress response history original data of the rigid bolt unit are imported and processed by using the excel data statistical tool to obtain the different road type accumulation statistical results and the full test mileage accumulation statistical results, as shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] Further, the results obtained by using the above process are as follows: for the same structure, identify which road surface has the greatest impact on bolt loosening in the same structure, identify the specific position of the most dangerous bolt in the same structure, and identify the bolt loosening degree within the full mileage range; for different structures, compare the advantages and disadvantages of the bolt loosening performance between structures, compare the bolt loosening performance improvement effect of the improvement scheme or performance factor, etc.

[0063] ​Note that the above merely describes preferred embodiments of the present application and the principles of the technology applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the claims.

Claims

1. A method of determining loosening of a bolt of a passenger vehicle body cantilever structure, characterized by, Comprise the following steps: A, based on the road spectrum of the body connection point load spectrum analysis; based on the test track, build a whole vehicle multi-body model, and extract the load spectrum of the body connection point by using virtual iteration method; the external load of the bolt unit is extracted by using the body CAE technology, and then the bolt is judged whether to move and the moving times are judged according to the corresponding criterion; based on the actual road load spectrum, the vibration performance of the structure is considered by using finite element technology, which can accurately reflect the bolt movement of different positions of the detailed structure, and the situation is reflected in a certain quantitative form, which can accurately reflect the trend of bolt movement of different bolts in the same structure and different structures; B, based on the load time history analysis of the fastening bolt of the cantilever structure based on the load spectrum of the body connection point; based on the load spectrum of the body connection point, the cantilever structure is loaded on the full interior white body model, and the connecting bolt between them is connected by a rigid spring, and the modal transient dynamic analysis is carried out, and the full road longitudinal and two radial internal force response spectrum of the rigid spring are extracted; B1, the force / torque signals of all connection points FX, FY, FZ, MX, MY and MZ of the white body are used as the load input conditions; B2, the full interior white body grid model is used to load the cantilever structure assembly grid model to be evaluated, and the bolt connection between the cantilever structure assembly and the white body grid is connected by a rigid spring unit; B3, the transient dynamics response analysis based on the free modal of the above grid model is calculated, and the longitudinal and two radial force response time history curve signals of the bolt rigid spring unit are obtained; C, based on the load time history of the fastening bolt of the cantilever structure, the bolt movement is determined; the rigid spring full road internal force response spectrum sample at each time is determined by formula, such as bolt radial force*friction coefficient < bolt radial internal force, which is considered as moving 1 time, otherwise it is considered as no movement; the judgment basis is that the bolt pre-tightening force minus the longitudinal load external force, multiplied by the friction coefficient, the force value obtained is the critical value of bolt movement, if the bolt longitudinal load external force is greater than the critical value, it is considered that the bolt moves 1 time; otherwise, it is considered that the bolt does not move; all sample points in the longitudinal and two radial force response time history curve signals of the bolt rigid spring unit are determined according to the above determination basis, and the corresponding determination times are obtained; D, the total number of full road bolt movement is counted; All time samples are counted, including the sum of movement times of each different road in the test field, and the sum of movement times corresponding to all road responses, which is the final determination result; The statistical results are classified and accumulated according to different road types, and the whole test mileage is accumulated.

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