CAE analysis method of seat body pressure distribution based on forced displacement method

Abstract

The invention discloses a CAE analysis method for seat body pressure distribution based on a forced displacement method, which includes the following steps: firstly, combining the modeling data of the seat cover, determining the engineering data of the foam and the tension line; when modeling, in addition to the seat frame, plastic parts and foam, the cover and the tension line are also included, and the initial penetration between the foam and the cover is retained; forming a prestress file of the foam and the cover; simulating the tension line with a 1D spring unit; importing the formed prestress file into the established seat whole chair finite element model, and the final seat model includes the prestress of the cover with the tension line wrapping the foam; importing the dummy model; positioning the dummy; according to the initial position of the dummy, loading the forced displacement reaching the theoretical R point of the dummy to simulate the process of a person sitting on the seat, and setting the pressure output on the card.intfor; a total of ten steps. The simulation process is simple, the simulation result is more real and reliable, the seat development cost is reduced, the development cycle is shortened, and it is an effective means of early comfort verification in the seat development process.

Description

Technical Field

[0001] The invention belongs to the technical field of CAE of automobile seats, and in particular relates to a CAE analysis method for seat body pressure distribution based on a forced displacement method. Background Art

[0002] Car seats are one of the most important parts in cars. In automotive ergonomics, the body pressure distribution of car seats is tested to study several car seat structural factors that affect body pressure distribution. In the process of car seat structural design, attention is paid to these design points that affect body pressure distribution, and the pressure distribution at the interface between people and seats is made uniform and smooth by optimizing the structure, thereby improving riding comfort.

[0003] At present, the seat body pressure distribution is carried out by test methods, and the stress distribution is adjusted by combining the test pieces. The test cost is high and the rectification cycle is long. If it can be combined with the finite element method, by analyzing the characteristics of static body pressure distribution, the seat test cost can be reduced and the rectification cycle can be shortened, which is very necessary for product development. However, due to the limitations of the current finite element analysis method, there is a certain gap between the analysis results and the test results, so the traditional test method is usually used. Summary of the invention

[0004] Aiming at the defects of high cost and long cycle of traditional seat body pressure distribution test, a finite element method is proposed to predict the body pressure distribution of seat performance, so as to reduce the seat test cost, shorten the development cycle, and make the finite element analysis method more realistic and reliable.

[0005] To this end, the technical solution adopted by the present invention is: a CAE analysis method for seat body pressure distribution based on forced displacement method, comprising the following steps:

[0006] The first step is to establish a finite element model of the entire seat;

[0007] First, the engineering data of the foam and the suspension wire are determined based on the modeling data of the seat cover. When modeling, in addition to the seat frame, plastic parts, and foam, the cover and the suspension wire are also included, and the initial penetration between the foam and the cover is retained. The mesh size of the seat frame and plastic parts is 4 to 6 mm.

[0008] The second step is to form the prestress file of the foam and the face cover; the mesh size of the face cover and the foam is 8 to 12 mm, and the tension wire is used as the tension wire of the face cover, which is simulated by 1D spring unit;

[0009] First, establish dynamic relaxation contacts between the seat cushion foam and the seat cushion cover, and between the backrest foam and the backrest cover to eliminate initial penetration and simulate the state of the cover wrapping the foam. Then, set the prestress file of the output foam and the cover in the load concentration. Finally, set the card to start dynamic relaxation.

[0010] The third step is to import the prestress file generated in the second step into the finite element model of the whole seat established in the first step, replacing the foam and the cover in the original model. The final seat model includes the prestress of the cover with a tightening line wrapping the foam, which is more consistent with the state of the foam and the cover when the actual occupant sits on the seat;

[0011] Step 4: Import the dummy model;

[0012] First, adjust the dummy's H point according to the R point position of the seat, and adjust the position of the dummy's feet according to the heel point position. Then adjust the dummy's torso angle to 25.5-27.5° to simulate a person leaning on the backrest. Adjust the dummy's H point position along the positive Z direction and negative X direction so that the dummy's buttocks and back are 6-15mm apart from the seat cushion and backrest respectively. Ensure that the dummy does not come into contact with the seat at any possible contact position, including the seat headrest, backrest cover, and seat cushion cover.

[0013] Step 5: Positioning the dummy;

[0014] Comprehensively consider the contact between the dummy and the seat parts when sitting down, and retain the contact part between the dummy and the seat, and give the dummy a rigid material; among them, the contact between the dummy and the face cover is set separately, and the pressure is output;

[0015] Step 6: Keep the elasticity and plasticity of the seat cover, foam, cushion spring, backrest spring, and plastic parts, and set the seat frame to be rigid;

[0016] Step 7. According to the initial position of the dummy, load the forced displacement to reach the theoretical R point of the dummy to simulate the process of a person sitting on the seat. Set the pressure output.intfor on the card.

[0017] Step 8: Submit Dyna calculation;

[0018] Step 9. Read the .intfor result and check the pressure distribution.

[0019] The tenth step is to evaluate the softness, hardness, stiffness and comfort design of the seat through maximum pressure, average pressure, contact area and maximum pressure gradient.

[0020] As a preferred embodiment of the above scheme, in the first step, since the face cover exhibits strong anisotropy, anisotropic material card simulation is required; the grid size of the seat frame and plastic parts is 5mm, and the grid size of the face cover and foam is 10mm.

[0021] Further preferably, in the fourth step, the dummy model can select a suitable dummy according to the situation; the dummy position is adjusted, including the contact between the dummy's feet and the pedals, the pedals are the main surface, and the feet are the secondary surface; the dummy's buttocks and back are separated from the seat cushion and the backrest by 8 mm respectively, and the dummy's torso angle is adjusted to 27.5°, so that the torso angle is 2.5° larger than the theoretical torso angle.

[0022] Further preferably, in the fifth step, the position and posture of the dummy are the theoretical position and posture of the occupant, and the seat foam is in an initial state, so the dummy and the seat are in an interference state, and the seat foam needs to be pressed into the actual shape by simulating the process of an actual occupant sitting on the seat.

[0023] More preferably, in the sixth step, the path to the theoretical R point is calculated based on the initial H point of the dummy, and the forced displacement is set.

[0024] More preferably, in the sixth step, the contact parts between the dummy and the seat are the buttocks, thighs and torso.

[0025] More preferably, in the seventh step, the calculation is performed by LS-Dyna software.

[0026] More preferably, in the eighth step, it is implemented by Hyperview software.

[0027] Beneficial effects of the present invention:

[0028] (1) When establishing the finite element model of the entire seat, usually only the seat frame, plastic parts and foam are considered, and the initial penetration between the foam and the cover is ignored. As a result, the final seat model does not match the actual state of the occupant sitting on the seat, and the finite element analysis results are inconsistent with the actual test results;

[0029] When establishing the finite element model in step 1, the present invention determines the engineering data of the foam and the suspension wire through the modeling data of the seat cover, and adds the seat cover and the suspension wire during modeling, so as to retain the initial penetration between the foam and the seat cover. Therefore, modeling is the key innovation of the finite element analysis method.

[0030] (2) On this basis, step 2 is added to form a prestress file of the foam and the face cover, so that the prestress file formed in the second step can be imported into the finite element model of the whole seat established in the first step to replace the foam and face cover in the original model. The final seat model includes the prestress of the face cover with a tightening line wrapping the foam, which is more consistent with the state of the foam and face cover when the actual occupant sits on the seat;

[0031] (3) Usually, the definition of the dummy's torso angle is equal to the theoretical torso angle. In step 4 of the present invention, the dummy's torso angle is adjusted to 25.5 to 27.5 in order to better simulate the process of a person leaning on the backrest.

[0032] (4) Usually, when performing finite element model analysis of a seat, when performing the dummy positioning in the fifth step, only the contact between the dummy and the seat components during the sitting process is considered; in this step, the present invention adds "separately setting the contact between the dummy and the face cover and outputting the pressure" in order to obtain the maximum pressure, average pressure, contact area, and maximum pressure gradient in the ninth step, thereby evaluating the softness, hardness, stiffness, and comfort design of the seat;

[0033] (5) In the sixth step, the elastic-plastic properties of the seat cover, foam, cushion spring, backrest spring, and plastic parts are retained, and the seat frame is set to be rigid; the elastic-plastic properties of the seat frame have little effect on the pressure distribution results. Setting it to be rigid, retaining the anisotropy of the cover, the compression properties of the foam, and the elastic-plastic properties of the spring can more realistically reflect the pressure distribution results;

[0034] (6) In the seventh step, a forced displacement is loaded to reach the theoretical R point of the dummy according to the initial position of the dummy to simulate the process of a person sitting on the seat. The card sets the pressure output .intfor to more realistically simulate the actual process of a person sitting on the seat.

[0035] In summary, this finite element analysis method uses the forced displacement method to simulate the seat body pressure distribution. The simulation process is simple, the simulation results are more realistic and reliable, the seat development cost is reduced, the development cycle is shortened, and it is an effective means of early comfort verification in the seat development process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a simulation diagram of the initial penetration between the foam and the face cover (the bright white area in the figure is the interference area).

[0037] Figure 2 This is an illustration of the model after the dummy positioning is completed.

[0038] Figure 3 This is the pressure distribution structure diagram of the forced displacement method. DETAILED DESCRIPTION

[0039] The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings:

[0040] A CAE analysis method for seat body pressure distribution based on a forced displacement method comprises the following steps:

[0041] The first step is to establish a finite element model of the entire seat.

[0042] First, the engineering data of the foam and the suspension wire are determined based on the modeling data of the seat cover. When modeling, in addition to the seat frame, plastic parts, and foam, the cover and the suspension wire are also included, and the initial penetration between the foam and the cover is retained, such as Figure 1 As shown. The mesh size of the seat frame and plastic parts is 4-6 mm, the mesh size of the face cover and foam is 8-12 mm, and the tension wire is used as the tension wire of the face cover and is simulated by 1D spring unit;

[0043] In the first step, since the face cover exhibits strong anisotropy, it is best to use anisotropic material card simulation; the mesh size of the seat frame and plastic parts is preferably 5mm, and the mesh size of the face cover and foam is preferably 10mm.

[0044] The second step is to form the prestressed file of the foam and the cover.

[0045] First, dynamic relaxation contact is established between the seat cushion foam and the seat cushion cover, and between the backrest foam and the backrest cover to eliminate initial penetration and simulate the state of the cover wrapping the foam. Then, the prestress file of the output foam and the cover is set in the load concentration. Finally, the card setting starts dynamic relaxation.

[0046] The third step is to import the prestressed material generated in the second step into the finite element model of the entire seat established in the first step, replacing the foam and cover in the original model. The final seat model includes the prestressed foam wrapped in the cover with a tensioning line, which is more consistent with the state of the foam and cover when the actual occupant sits on the seat.

[0047] Step 4: Import the dummy model.

[0048] First, adjust the dummy's H point (the connection point between the torso and thigh in the human body model, i.e., the hip point) according to the position of the seat's R point (the seating reference point of the car), and adjust the position of the dummy's feet according to the position of the heel point. Then adjust the dummy's torso angle to 25.5-27.5° to simulate a person leaning on the backrest. Adjust the dummy's H point position along the positive Z direction and negative X direction so that the dummy's buttocks and back are separated from the seat cushion and backrest by 6-15 mm respectively, ensuring that the dummy does not come into contact with the seat at any possible contact point, including the seat headrest, backrest back cover, and seat cushion surface cover.

[0049] Adjust the position of the dummy, also including the contact between the dummy's feet and the pedals, with the pedals as the primary surface and the feet as the secondary surface; the dummy's buttocks and back are 8 mm separated from the seat cushion and backrest respectively, and the dummy's torso angle is adjusted to 27.5°, making the torso angle 2.5° larger than the theoretical torso angle.

[0050] Step 5: Positioning the dummy.

[0051] Consider the contact between the dummy and the seat parts during the sitting process, keep the contact part between the dummy and the seat, and give the dummy rigid materials; the contact between the dummy and the face cover is set separately, and the pressure is output. It is best that the dummy's position and posture are the theoretical position and posture of the occupant, and the seat foam is in the initial state, so the dummy and the seat are in an interference state. It is necessary to compress the seat foam to the actual shape by simulating the process of the actual occupant sitting on the seat, such as Figure 2 shown.

[0052] The sixth step is to retain the elasticity and plasticity of the seat cover, foam, seat cushion spring, backrest spring, and plastic parts, and set the seat frame to be rigid; the elasticity and plasticity of the seat frame have little effect on the pressure distribution results, and setting it to be rigid and retaining the anisotropy of the cover, the compression performance of the foam, and the elasticity and plasticity of the spring can more realistically reflect the pressure distribution results.

[0053] Step 7. According to the initial position of the dummy, load the forced displacement to reach the theoretical R point of the dummy to simulate the process of a person sitting on the seat. Set the pressure output.intfor on the card; preferably, calculate the path to the theoretical R point based on the initial H point of the dummy and set the forced displacement. Due to the different dummies selected, the contact parts may be different. Select the retained part according to the situation. The contact parts between the dummy and the seat imported this time can be the buttocks, thighs and torso. Retain the appropriate dummy part. A smaller dummy may have the knees in contact with the seat cushion, so the retained part can be selected according to the size of the dummy.

[0054] Step 8: Submit dyna calculation; preferably, the calculation is performed using LS-Dyna software.

[0055] Step 9. Read the .intfor result and check the pressure distribution; preferably, this can be done through Hyperview software.

[0056] Step 10: Evaluate the softness, hardness, stiffness and comfort design of the seat through maximum pressure, average pressure, contact area and maximum pressure gradient. Figure 3 shown.

[0057] Maximum pressure: The maximum value of all pressure test points in the contact area between the human body and the cushion, which reflects the softness and hardness of the cushion and can also find abnormal value points during the test;

[0058] Average pressure: The average value of all pressure points on the contact surface between the human body and the cushion, which can reflect the stiffness characteristics of the cushion, and has certain manifestations for different materials, contact cut-off shapes, etc.

[0059] Contact area: the sum of the effective contact areas between the human body and the seat cushion. When determined by the tester, the size of the contact area directly affects the amplitude of the average pressure;

[0060] Maximum pressure gradient: The size of the pressure gradient value in the contact area can reflect whether the pressure distribution transition is slow or not. A larger transition will cause muscle stimulation and bring discomfort.

Claims

1. A CAE analysis method for seat body pressure distribution based on forced displacement method, characterized in that: The following steps are involved: The first step is to establish a finite element model of the entire seat; First, the engineering data of the foam and the suspension wire are determined based on the modeling data of the seat cover. When modeling, in addition to the seat frame, plastic parts, and foam, the cover and the suspension wire are also included, and the initial penetration between the foam and the cover is retained. The mesh size of the seat frame and plastic parts is 4 to 6 mm, and the mesh size of the cover and foam is 8 to 12 mm. The suspension wire is used as the tension wire of the cover and is simulated with a 1D spring unit. The second step is to form the prestressed file of the foam and the face cover; First, establish dynamic relaxation contacts between the seat cushion foam and the seat cushion cover, and between the backrest foam and the backrest cover to eliminate initial penetration and simulate the state of the cover wrapping the foam. Then, set the prestress file of the output foam and the cover in the load concentration. Finally, set the card to start dynamic relaxation. The third step is to import the prestress file generated in the second step into the finite element model of the whole seat established in the first step, replacing the foam and the cover in the original model. The final seat model includes the prestress of the cover with a tightening line wrapping the foam, which is more consistent with the state of the foam and the cover when the actual occupant sits on the seat; Step 4: Import the dummy model; First, adjust the dummy's H point according to the R point position of the seat. The R point is the seat reference point of the car, and the H point is the connection point between the torso and the thigh in the human body model. Adjust the position of the dummy's feet according to the heel point position, and then adjust the dummy's torso angle to 25.5-27.5° to simulate a person leaning on the backrest. Adjust the dummy's H point position along the positive Z direction and the negative X direction so that the dummy's buttocks and back are separated from the seat cushion and backrest by 6-15mm respectively, ensuring that the dummy does not come into contact with the seat at any possible contact position, including the seat headrest, backrest cover, and seat cushion cover. Step 5: Positioning the dummy; Comprehensively consider the contact between the dummy and the seat parts when sitting down, and retain the contact part between the dummy and the seat, and give the dummy a rigid material; among them, the contact between the dummy and the face cover is set separately, and the pressure is output; Step 6: Keep the elasticity and plasticity of the seat cover, foam, cushion spring, backrest spring, and plastic parts, and set the seat frame to be rigid; Step 7. According to the initial position of the dummy, load the forced displacement to reach the theoretical R point of the dummy to simulate the process of a person sitting on the seat. Set the pressure output.intfor on the card. Step 8: Submit Dyna calculation; Step 9. Read the .intfor result and check the pressure distribution. The tenth step is to evaluate the softness, hardness, stiffness and comfort design of the seat through maximum pressure, average pressure, contact area and maximum pressure gradient.

2. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1, characterized in that: In the first step, since the face cover exhibits strong anisotropy, an anisotropic material card simulation is required; the mesh size of the seat frame and plastic parts is 5mm, and the mesh size of the face cover and foam is 10mm.

3. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the fourth step, adjust the position of the dummy, including the contact between the dummy's feet and the pedals, with the pedals as the primary surface and the feet as the secondary surface; the dummy's buttocks and back are separated by 8mm from the seat cushion and backrest respectively, and the dummy's torso angle is adjusted to 27.5°.

4. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the fifth step, the dummy's position and posture are the occupant's theoretical position and posture, and the seat foam is in its initial state, so the dummy and the seat are in an interference state. The seat foam needs to be pressed into its actual shape by simulating the process of an actual occupant sitting on the seat.

5. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the sixth step, the path to the theoretical R point is calculated based on the dummy's initial H point, and the forced displacement is set.

6. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the sixth step, the contact points between the dummy and the seat are the hips, thighs, and torso.

7. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the seventh step, calculations are performed by LS-Dyna software.

8. The CAE analysis method for seat body pressure distribution based on forced displacement method according to claim 1 is characterized in that: In the eighth step, it is achieved through Hyperview software.

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