At present, the most representative foreign law governing the rollover safety of buses is ECER66 “Regulations on the Approval of Large Passenger Cars with Regard to Superstructure Strength”. Five kinds of verification methods are provided in the regulations: Basic Certification Method, Vehicle Tipping Test; Equivalent certification method, section tipping test of car body; Equivalent certification method, quasi-static load test of car body section; Equivalent certification method, quasi-static calculation based on test parts; equivalent certification method, computer simulation Car tipping test. In China, GB/T17578-1998 “Strength Requirements for Superstructure of Passenger Cars” was also developed with reference to ECE R66. Due to the high cost of actual vehicle rollover tests, the existing standards are not mandatory standards. Only a handful of domestic passenger car companies in China have done such tests because of the need for passenger car export certification. General bus companies only do static loading tests and use CAE software system to do dynamic and static simulation test of passenger cars.

The vehicle rollover test is an objective evaluation method, but the rollover test is a non-repeatable, destructive test. Each vehicle or sample can only be used once. In the development process of a passenger car, it often fails to succeed once. Tests lead to long cycle times and high costs. Therefore, in the passenger car design stage, using the finite element simulation analysis method for the passenger vehicle's tipping test simulation, safety evaluation and improved design not only can reduce the number of actual vehicle tests, but also shorten the development cycle and reduce costs. Since the bus industry is mostly small-batch, multi-variety production, calculation and simulation analysis methods are particularly important for bus development. However, whether it is a real vehicle test or a computer simulation test, the test procedures and test procedures must be conducted in accordance with the requirements of laws and standards. Only the simulation model validated by the actual vehicle rollover test can more truly reflect the dynamic response of the real vehicle during the rollover process. On this basis, the structural optimization and improvement can ensure its reliability and accuracy, and can be effectively evaluated. The body structure safety performance of the passenger car during the tilting test.

This article is based on a model of a large passenger vehicle that has undergone a rollover test at the National Bus Quality Supervision and Inspection Center. The finite element simulation analysis method was used to establish the vehicle's finite element model and perform rollover simulation analysis. The reliability and effectiveness of the passenger car rollover simulation model are verified by the real vehicle rollover test results. Based on the simulation and test results, a feasible scheme for improving the safety of the passenger car rollover body structure is proposed.

When building the vehicle's finite element model, the CAD 3D model of each part of the vehicle provided by the manufacturer is stored as an IGES format file, and the geometry of the part is input through the IGES format data conversion interface of the finite element simulation preprocessing software (HyperMesh). The lines and faces are divided into grids. The meshed model is in good agreement with the CAD model's appearance, and uses a uniform spatial coordinate, which is beneficial to the assembly of the finite element model of each component.

The passenger car body skeleton is composed of a large number of different sections of welded steel profiles. It is a typical space frame structure. In the modeling process, the unit type of each component is a shell element. Based on the results of the actual vehicle collision, the existing structure is rationally simplified according to the stress and deformation conditions, such as components of the engine, transmission, transmission shaft, etc. In the tipping test, their shape and structure do not substantially affect the calculation. As a result, rigid masses are generally used instead, and some of the process holes, mounting holes, bosses, and flanges on the load bearing structure are also ignored. The tire and suspension are assembled by establishing a cylindrical hinge unit between the wheel center and the axle. Since the suspension and the body assembly, the powertrain and the frame are generally connected by elastic elements, springs with different stiffnesses are used. The unit is connected; the various types of car body skeletons are connected by common nodes or spot welding simulations, and the weld length is equivalent to the actual weld length. The material of the car body skeleton is modeled by a piecewise linear plastic material model, and its stress-strain curve is obtained through a uniaxial tensile test of the material. The final vehicle tipping finite element simulation model was established as shown in 1.

The boundary conditions are defined in accordance with the requirements of the standard and the rollover situation of the actual vehicle. Automatic single-face contact is adopted between the body parts, and the contact between the body and the tilting platform and the ground adopts automatic surface-surface contact, in which the friction coefficient of the set surface is 0.7. The distance of the reversing platform to the ground is 800 mm, and the wheel baffle height At 80mm, the vertical longitudinal center plane (VLCP) of the passenger car is parallel to the axis of rotation of the tilting platform. The tilting test process is calculated using the finite element Post-processing software LS-DYNA widely used at home and abroad. During the simulation, the tilting platform rotates around the horizontal plane at an angular velocity of 0.04 rad/s (standard requirement does not exceed 0.087 rad/s). Shaft rotation.

When the vehicle reaches the unstable equilibrium angle, the turning platform stops rotating and the passenger car will tilt from the unstable equilibrium angle to the ground by its own gravity.

As the bus was tested at the National Vehicle Quality Supervision and Inspection Center of Chongqing Vehicle Inspection and Research Institute, a real vehicle rollover test was conducted. Therefore, the vehicle deformation, column deformation, vehicle acceleration response, and actual vehicle rollover test results obtained from simulation results were obtained. Data comparison to verify the reliability of the simulation model.

1) Vehicle deformation characteristics. These are the contrast angles of the unstable equilibrium angle during the tilting of the entire vehicle and the deformation of the vehicle body after the collision of the entire vehicle. The angles of unstable balance between test and simulation were 35.2° and 35.8°, respectively. At the end of the collision, the simulation model and the actual vehicle's tilted vehicle deformation results are very similar, the vehicle deformation is relatively large, the top structure and the body column waist strength is weak, especially at the waist of the column there is a large plastic hinge deformation, resulting in The intrusion of the upper structure of the bus was large.

2) Evaluation of occupant living space. During the actual vehicle rollover test, the intrusion of the column was measured by a deformation gauge installed next to the column. The position of the floor above the occupant's foot at a height of 1250 mm is the highest position of the living space. The intrusion amount in the simulation can be obtained directly by measuring the amount of change in the relative distance between the point and the longitudinal plane of the vehicle.

Table 1 shows the comparison of the intrusion amount at the measurement point of the highest position of each column of the test and simulation results. By comparison, the change trend of the deformation amount of the test and simulation results is basically the same. The simulation analysis of the deformation amount is smaller than the test result. The maximum error is 11.2%, which is much lower than the 20% error limit agreed by everyone in the industry. The distance between the maximum intrusion position of the right column and the living space of the occupant is only 20mm, and the risk of serious injury to the occupants in the vehicle caused by a rollover accident is high.

3) Analysis of acceleration response. During the rollover collision process, the acceleration curve can comprehensively reflect the change process of the collision force experienced by the vehicle during the entire test process, and it is also convenient for understanding some internal structural factors in the rollover collision process. Therefore, in the simulation, Acceleration response is usually used to evaluate the structural crashworthiness of the car body, and the effectiveness and reliability of the simulation model are verified based on the degree of coincidence between the simulation deformation amount of the right-pillar position Z test deformation and the acceleration response curve of the simulation results.

For the acceleration response curve of the center of gravity of the bus within 300ms after the bus and the ground began to contact, the maximum acceleration and acceleration of the test and simulation occurred in the collision phase of the lower half of the vehicle body, which was 37g and 42g, respectively. After 105ms and 100ms after impacting the ground, the simulation curves and the experimental curves basically agree with each other. The maximum peak error is only 13.5%, which indicates that the established finite element simulation model can reflect the dynamics of the real vehicle in the tilting test. response.

4) Comprehensive analysis. The above relevant data shows that the simulation model can reflect the rollover situation of real vehicles, and the established rollover finite element simulation model is effective and can be used as a basic model for further structural optimization and improvement of the vehicle. The analysis results show that the rigidity of the column and the roof part of the vehicle model is seriously insufficient, resulting in a large plastic deformation at the position of the column waist, and the upper right side of the vehicle body intrudes into the riding room, especially the second right column is away from the crew. The minimum distance in space is only 20mm. Although the test was passed, the importer of the car proposed that if the quality of seats and air conditioners changes in the future and the height of the mass center of gravity changes, the 20mm figure will be more dangerous. Therefore, the safety of the vehicle's tipping body structure needs further improvement to reduce the severity of injury to the vehicle members when the vehicle is tipped.

5) Structural improvement design and evaluation. Based on the above analysis, in order to reduce the deformation of the entire vehicle during the tilting process, increase the living space of the occupants in the vehicle and improve the structural safety of the tipping body of the vehicle, the structural improvement design of the vehicle can improve the strength of the column waist. Consider the structural strength of the transition zone between the top beam and the side pillar. This article mainly carried out the partial structure enhancement design of the body column waist of this model. 5 is a deformed cloud image of a body section with an improved structure. The maximum measurement point of the second-column right-hand side of the occupant's living space corresponds to the intrusion amount at the measurement position on the column is reduced by 54mm, and the safety of the occupant's living space is improved. Improvements.

The finite element model of the passenger car was established by computer simulation method and the simulation analysis was carried out. The validity and reliability of the constructed finite element simulation model were verified by the actual vehicle tipping test data. Based on this, the structural safety of the passenger car was evaluated. And put forward improvement measures. The improved passenger car rollover structure safety has been greatly improved, reducing the risk of serious injury to the occupants of the vehicle. It shows that the use of computer simulation analysis of the passenger vehicle superstructure strength tipping test and improved design is very applicable and effective, it should be widely used in the passenger car industry to reduce development costs and shorten the development cycle.

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