Exhaust system gap simulation analysis method based on multi-body dynamics

Abstract

The present application relates to a kind of exhaust system gap simulation analysis method based on multi-body dynamics, including digital road creation: tire model is established, the surface layer of tire is separated from main body, 80-200 concentrated mass band is used to indicate the cord, steel wire, rubber in tire structure;Establish multi-body dynamics model, utilize hard point, mass, stiffness information and topological relationship information etc. to establish a complete multi-body dynamics model;Exhaust system flexibility;Multi-body dynamics model debugging: establish displacement monitoring: digital test field simulation: gap analysis.The exhaust system of the present application is flexibly handled, and the gap obtained by calculation is more accurate;Displacement monitoring is established between exhaust system and vehicle body, the node of small range area and center interface point are rigidly connected, and the displacement monitoring of exhaust system and vehicle body is more accurate;Exhaust system gap simulation analysis is carried out using virtual test field method, and the gap between exhaust system and vehicle body is determined at the early stage of design.

Description

Technical Field

[0001] This invention belongs to the field of automotive technology, specifically relating to a simulation analysis method for exhaust system clearance based on multibody dynamics. Background Technology

[0002] Currently, the spatial design between the exhaust system and the vehicle body remains a challenge in automotive exhaust system design.

[0003] Because the exhaust system is a suspension component, it undergoes overall and localized deformation and vibration during vehicle movement. Therefore, the clearance between the exhaust system and the vehicle body is difficult to determine. Generally, space is reserved based on experience, but this can result in an excessively large gap between the exhaust pipe and the body, affecting the vehicle's aesthetics. Alternatively, the clearance of the exhaust system can only be determined after real-vehicle testing at a proving ground, allowing for iterative optimization. This iterative cycle is very long, and both testing and cycle costs are high. Summary of the Invention

[0004] The purpose of this invention is to provide a simulation analysis method for exhaust system clearance based on multibody dynamics, so as to solve the problem of difficulty in controlling the arrangement distance between the exhaust system and the vehicle body.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A simulation analysis method for exhaust system clearance based on multibody dynamics includes the following steps:

[0007] A. Digital road surface creation:

[0008] Road surface scanning converts the geometric contours of the road surface into point cloud data. The point cloud data is then meshed to complete the fitting and verification of the digital road surface model and generate a CRG road surface model for ADAMAS simulation and recognition.

[0009] B. Tire model:

[0010] The tire's outer layer is separated from the main body, and 80-200 concentrated mass belt nodes are used to represent materials such as cord fabric, steel wire, and rubber in the tire structure. Springs and damping are added between the nodes.

[0011] C. Establish a multibody dynamics model:

[0012] A complete multibody dynamics model is established using information such as hard points, mass, stiffness, and topological relationships.

[0013] D. Flexibility of the exhaust system:

[0014] The exhaust system is made flexible using the modal synthesis method, and the inherent characteristics of the system and dynamic response are solved. The modal termination of the substructure is preserved as a modal including rigid body modes and elastic modes. Then the flexible exhaust system is imported into a multibody dynamics model.

[0015] E. Multibody dynamics model tuning: including suspension static characteristic tuning and suspension dynamic characteristic tuning;

[0016] F. Establish displacement monitoring:

[0017] G. Digital test field simulation:

[0018] Based on the completed vehicle multibody dynamics model, a digital test track road surface was added; according to the test track specifications, a digital test track simulation experiment was conducted; during the simulation, the vehicle was driven along the centerline of the road surface, and the vehicle speed was kept consistent with the test specifications.

[0019] H. Gap Analysis

[0020] After the simulation in step G is completed, the results of the corresponding displacement monitoring points in step F are extracted, and the displacement results in step F are used to further design the exhaust system based on feedback.

[0021] Further, in step A, a road surface scanning method using a 3D laser road surface scanner with the entire vehicle moving is employed.

[0022] Further, in step A, the grid size is 5mm × 5mm.

[0023] Further, in step D, the modal orders to be retained for each component are as follows: rigid body modes, retain 6 rigid body modes; elastic modes, if the number of external interface points is x and the number of elastic modes to be retained is y, then y = 6x + 30, and the cutoff frequency is 500 Hz.

[0024] Further, in step D, the external interface points are connected to the corresponding finite element mesh nodes using RBE2 elements, and each external interface point needs to be constrained in six directions of freedom.

[0025] Further, in step E, the static characteristics of the suspension are adjusted. Specifically, the vertical stiffness, longitudinal stiffness, lateral stiffness, and roll stiffness of the front and rear suspensions are simulated respectively. The experimental data are compared, and the parameter settings of the rubber bushings, springs, and stabilizer bars are fine-tuned so that the simulated suspension stiffness results are consistent with the experimental values.

[0026] Further, step E, suspension dynamic characteristic adjustment, specifically involves adjusting the damping characteristics of the bushings and shock absorbers during the suspension's dynamic excitation process.

[0027] Further, in step F, displacement monitoring is established. If the stiffness of the position close to the vehicle body and the exhaust system is low, the influence caused by the deformation of the exhaust system cannot be ignored, and displacement monitoring needs to be established in the corresponding area. If the stiffness of the position close to the vehicle body and the exhaust system is high, the influence of the deformation of the exhaust system can be ignored, and displacement monitoring for the entire exhaust system can be established.

[0028] Furthermore, at the location closest to the exhaust system and the vehicle body, a point is selected on the surface of the exhaust system. Two to three rings of nodes are selected near the selected point and rigidly connected to this node. This node is used as the external interface point for exhaust system displacement monitoring. At the corresponding location on the vehicle body, another point is selected using the same method as the external interface point for vehicle body displacement monitoring. Marker reference points for corresponding components are established using the external interface points between the exhaust system and the vehicle body, and displacement monitoring is then established.

[0029] Furthermore, displacement monitoring is established at the center of gravity of the exhaust system. A marker reference point a, belonging to the exhaust system itself, is established at the center of gravity of the exhaust system, and reference point a moves with the entire exhaust system. A marker reference point b, belonging to the vehicle body, is established at the center of gravity of the exhaust system, and reference point b moves with the vehicle body. The movement of marker reference point a relative to marker point b, including three-dimensional displacement and three-dimensional rotation, is monitored to reconstruct the overall spatial movement of the exhaust system and to determine the minimum distance between the exhaust system and the vehicle body.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention innovatively treats the exhaust system flexibly, so that the deformation of the exhaust system can be taken into account when calculating the gap between the exhaust system and the vehicle body, resulting in a more accurate calculated gap;

[0032] 2. Innovatively, displacement monitoring is established between the exhaust system and the vehicle body. A small area of ​​nodes is rigidly connected to the central interface point, so that the external interface point can reflect the deformation within the area. This makes the displacement monitoring of the exhaust system and the vehicle body more accurate.

[0033] 3. Innovatively utilizes virtual test track method for exhaust system clearance simulation analysis; currently, exhaust system clearance is designed based on experience, or can only be determined after actual vehicle testing at the test track; this application utilizes virtual test track method, which can determine the clearance between the exhaust system and the vehicle body in the early design stage, and can support the forward design of the clearance between the exhaust system and the vehicle body. Attached Figure Description

[0034] 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.

[0035] Figure 1 Flowchart of the steps for simulation analysis of exhaust system clearance based on multibody dynamics;

[0036] Figure 2 Schematic diagram of exhaust system model;

[0037] Figure 3 Schematic diagram of digital road surface scanning;

[0038] Figure 4 Ftire tire illustration;

[0039] Figure 5 Multibody dynamics model of a vehicle with an exhaust flexible body system. Detailed Implementation

[0040] The present invention will be further described below with reference to embodiments:

[0041] 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.

[0042] 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.

[0043] This invention provides a multibody dynamics-based method for simulating and analyzing the clearance of an exhaust system, comprising the following steps:

[0044] The first step, digital road surface creation:

[0045] The road surface is scanned using a 3D laser road surface scanning method with the whole vehicle moving, and the road surface geometric contour is scanned into point cloud data. The point cloud data is then meshed by analysis and processing software to complete the fitting and verification of the digital road surface model, and generate a CRG road surface model for ADAMAS simulation and recognition with a mesh size of 5mm×5mm.

[0046] Step 2, tire model:

[0047] The Ftire tire model is suitable for endurance simulation. Its modeling method separates the tire's outer layer from the main body, using 80-200 concentrated mass belt nodes to represent materials such as the tire's cords, steel wires, and rubber. Springs and dampers are added between these nodes to describe the tire's vibration and lateral slip characteristics. Therefore, tire tests are conducted using actual tires to obtain the corresponding Ftire tire model.

[0048] The third step is to establish a multibody dynamics model:

[0049] A complete multibody dynamics model is established using information such as hard points, mass, stiffness, and topological relationships.

[0050] The fourth step is to make the exhaust system more flexible.

[0051] The deformation of the exhaust system in a vehicle has a significant impact on the system's dynamic characteristics. To make the multibody dynamics model in the digital simulation technology of the whole vehicle more accurate, it is necessary to consider the influence of component deformation on the motion of the entire system. Therefore, the modal synthesis method can be used to make the exhaust system more flexible, which means decomposing a complex structure into several simpler substructures. Based on understanding the vibration characteristics of each substructure, these substructures are synthesized into a whole structure according to the coordination conditions on the mating surfaces. Then, the vibration mode of the whole structure is obtained by using the vibration mode of each substructure. Using this method, the inherent characteristics of the system and dynamic response analysis are performed. The modes of the substructures that need to be saved are divided into rigid body modes and elastic modes. The modal orders that need to be retained for each component are as follows: Rigid body modes: retain 6 rigid body modes; Elastic modes: if the number of external interface points is x and the number of elastic modes to be retained is y, then y = 6x + 30 (cutoff frequency is 500 Hz). This can effectively reduce the degrees of freedom without changing the physical nature of the system. Then, the flexible exhaust system is imported into the multibody dynamics model, so that the deformation of the exhaust system can be effectively taken into account during the simulation.

[0052] Tables 1 and 2 specify the mesh size and quality requirements for each component when meshing and forming a flexible body. Mesh generation must be strictly performed according to the control indicators in the tables. In addition, external interface points and corresponding finite element mesh nodes are connected using RBE2 elements, and each external interface point needs to be constrained in six directions of freedom.

[0053] Table 1. Unit Type and Unit Size Requirements

[0054]

[0055] Table 2 Mesh Quality Requirements

[0056]

[0057] Step 5: Debugging the multibody dynamics model:

[0058] Static suspension characteristic tuning: Based on suspension kinematics and elastic kinematics theory, when a wheel bounces up and down, it causes changes in wheel alignment angles and the forces on the links. Simulations of vertical stiffness, longitudinal stiffness, lateral stiffness, and roll stiffness are performed on the front and rear suspensions respectively. The data are compared with experimental data, and the parameter settings of the rubber bushings, springs, and stabilizer bars are fine-tuned to ensure that the simulated suspension stiffness results are consistent with the experimental values. It is particularly important to consider the nonlinear region of suspension stiffness and the buffer block clearance when simulating suspension stiffness, and to compare the simulated and experimental suspension stiffness values ​​as closely as possible.

[0059] Suspension dynamic characteristic tuning: Since there are nonlinear components such as rubber bushings and shock absorbers in the suspension structure, the suspension characteristics change due to the influence of damping during dynamic excitation. Virtual test track simulation is a virtual dynamic driving simulation process of a car, so it is necessary to tune the damping characteristics of the bushings and shock absorbers.

[0060] Step 6: Establish displacement monitoring:

[0061] There are two methods for establishing displacement monitoring. If the stiffness of the position close to the vehicle body and the exhaust system is low, the influence caused by the deformation of the exhaust system cannot be ignored, and displacement monitoring needs to be established in the corresponding area, as shown in Scheme 1 below. If the stiffness of the position close to the vehicle body and the exhaust system is high, the influence of the deformation of the exhaust system can be ignored, and displacement monitoring can be established for the entire exhaust system.

[0062] 1. A separate displacement monitor can be added near the exhaust system and vehicle body to monitor changes in the distance between them. The main method is to select a point on the surface of the exhaust system at the closest point to the vehicle body. Since the exhaust system is a flexible body composed of a mesh, the mesh nodes may be distorted, affecting the results. Therefore, select 2-3 rings of nodes near the selected point and connect them rigidly. This way, the node reflects the deformation within a small area, which is more accurate. Use this node as the external interface point for exhaust system displacement monitoring. On the corresponding location on the vehicle body, select another point using the same method as the external interface point for vehicle body displacement monitoring. Establish marker reference points for the corresponding components using the external interface points between the exhaust system and the vehicle body, and then establish displacement monitoring.

[0063] 2. Displacement monitoring can be established at the center of gravity of the exhaust system. A marker reference point 'a' belonging to the exhaust system itself can be established at the center of gravity of the exhaust system, and reference point 'a' moves with the entire exhaust system. A marker reference point 'b' belonging to the vehicle body can be established at the center of gravity of the exhaust system, and reference point 'b' moves with the vehicle body. By monitoring the movement of marker reference point 'a' relative to marker point 'b', including three-dimensional displacement and three-dimensional rotation, the overall spatial movement of the exhaust system can be reconstructed. Therefore, the minimum distance between the exhaust system and the vehicle body can be determined.

[0064] Step 7, Digital Testbed Simulation:

[0065] Based on the debugged multibody dynamics model of the vehicle, a digital test track surface was added. Digital test track simulation experiments were conducted according to the test track specifications. During the simulation, the vehicle was driven along the centerline of the road surface at a speed consistent with the test specifications.

[0066] Step 8 Gap Analysis

[0067] After the simulation in step seven is completed, the results of the corresponding displacement monitoring points in step six are extracted. Such displacement results can cover all the road surfaces of the enhanced durability test track. Therefore, by using the displacement results in step six to further design the exhaust system, a refined design can be achieved even when there is no test vehicle available in the early stages.

[0068] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A simulation analysis method for exhaust system clearances based on multibody dynamics, characterized in that, Includes the following steps: A. Digital road surface creation: Road surface scanning converts the geometric contours of the road surface into point cloud data. The point cloud data is then meshed to complete the fitting and verification of the digital road surface model and generate a CRG road surface model for ADAMAS simulation and recognition. B. Tire model: The tire's outer layer is separated from the main body, and 80-200 concentrated mass belt nodes are used to represent the tire's cord, steel wire, and rubber materials. Springs and damping are added between the nodes. C. Establish a multibody dynamics model: A complete multibody dynamics model is established using information on hard points, mass, stiffness, and topological relationships. D. Flexibility of the exhaust system: The exhaust system is made flexible using the modal synthesis method, and the inherent characteristics of the system and dynamic response are solved. The modal termination of the substructure is preserved as a modal including rigid body modes and elastic modes. Then the flexible exhaust system is imported into a multibody dynamics model. E. Multibody dynamics model tuning: including suspension static characteristic tuning and suspension dynamic characteristic tuning; F. Establish displacement monitoring: G. Digital test field simulation: Based on the completed vehicle multibody dynamics model, a digital test track road surface was added; according to the test track specifications, a digital test track simulation experiment was conducted; during the simulation, the vehicle was driven along the centerline of the road surface, and the vehicle speed was kept consistent with the test specifications. H. Gap Analysis After the simulation in step G is completed, the results of the corresponding displacement monitoring points in step F are extracted, and the displacement results in step F are used to further design the exhaust system based on feedback. Step A: The road surface is scanned using a 3D laser road surface scanning method with the whole vehicle moving; the grid size is 5mm×5mm. Step D: The modal orders to be retained for each component are as follows: rigid body modes, retain 6 rigid body modes; elastic modes, if the number of external interface points is x and the number of elastic modes to be retained is y, then y = 6x + 30, and the cutoff frequency is 500 Hz; external interface points are connected to the corresponding finite element mesh nodes using RBE2 elements, and each external interface point needs to constrain six degrees of freedom in six directions; Step E, suspension static characteristic tuning, specifically involves: simulating the vertical stiffness, longitudinal stiffness, lateral stiffness, and roll stiffness of the front and rear suspensions respectively, comparing the experimental data, and fine-tuning the parameter settings of the rubber bushings, springs, and stabilizer bars to ensure that the simulated suspension stiffness results are consistent with the experimental values; suspension dynamic characteristic tuning, specifically involves: adjusting the damping characteristics of the bushings and shock absorbers during dynamic excitation of the suspension. Step F: Establish displacement monitoring. If the stiffness of the area near the vehicle body and exhaust system is low, the impact of exhaust system deformation cannot be ignored, and displacement monitoring needs to be established in the corresponding area. If the stiffness of the area near the vehicle body and exhaust system is high, the impact of exhaust system deformation can be ignored, and displacement monitoring for the entire exhaust system can be established. At the position closest to the vehicle body, select a point on the surface of the exhaust system, and select 2-3 nodes near the selected point and connect them to the node using a rigid connection. Use this node as the external interface point for exhaust system displacement monitoring. At the corresponding position on the vehicle body, select another point using the same method as the external interface point for vehicle body displacement monitoring. Use the external interface points between the exhaust system and the vehicle body to establish marker reference points for the corresponding components, and establish displacement monitoring. Displacement monitoring is established at the center of gravity of the exhaust system. A marker reference point 'a' belonging to the exhaust system itself is established at the center of gravity of the exhaust system, and reference point 'a' moves with the overall movement of the exhaust system. A marker reference point 'b' belonging to the vehicle body is established at the center of gravity of the exhaust system, and reference point 'b' moves with the vehicle body. The movement of marker reference point 'a' relative to marker point 'b', including three-dimensional displacement and three-dimensional rotation, is monitored to reconstruct the overall spatial movement of the exhaust system and to determine the minimum distance between the exhaust system and the vehicle body.

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