Finite element analysis method of seat body pressure distribution based on gravity method

Abstract

This invention discloses a finite element analysis method for seat body pressure distribution based on gravity, comprising the following steps: First, combining the shape data of the seat cover, the engineering data of the foam and suspension lines are determined; during modeling, in addition to the seat frame, plastic parts, and foam, the cover and suspension lines are also included, and the initial penetration of the foam and cover is preserved; a prestress file for the foam and cover is generated; the suspension lines are simulated using 1D spring elements; the generated prestress file is imported into the established finite element model of the entire seat, and the final seat model includes the prestress of the foam wrapped by the cover with suspension lines; a dummy model is imported; the dummy is positioned; an acceleration at an angle of 40-50° to the z-direction is applied; a total of ten steps. The simulation process is simple, the simulation results are more realistic and reliable, reducing seat development costs and shortening the development cycle, and is an effective means of early comfort verification in the seat R&D process.

Description

Technical Field

[0001] The invention belongs to the technical field of CAE of automobile seats, and in particular relates to a finite element analysis method of seat body pressure distribution based on a gravity 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 finite element analysis method for seat body pressure distribution based on gravity 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] The contact between the dummy and the seat components during the sitting process is comprehensively considered, so as to establish contact; wherein the contact between the dummy and the face cover is set separately, and the pressure is output;

[0015] Step 6: Load an acceleration that is 40-50° with the z-axis. Start with 3g acceleration and gradually adjust to 1g acceleration curve to simulate the process of a person sitting on a seat. Set the pressure output on the card.intfor;

[0016] Step 7: Submit Dyna calculation;

[0017] Step 8. Read the calculation results, derive the dummy's H point in the calculation results, and compare the H point result with the dummy's theoretical R point. If the coordinates of x, y, and z are controlled within ±10mm, the result is valid; if the coordinate error does not meet the requirements, the loading acceleration needs to be adjusted.

[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] It is further preferred that, in the fourth step, the imported dummy model is of type HIII50, and a suitable dummy can be selected 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 direction of the loaded acceleration forms an angle of 45° with the Z direction to simulate a process of a person leaning towards a seat.

[0024] More preferably, in the seventh step, the calculation is performed by LS-Dyna software.

[0025] More preferably, in the eighth step, it is implemented by Hyperview software.

[0026] Beneficial effects of the present invention:

[0027] (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;

[0028] 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.

[0029] (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 the 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 the face cover when the actual occupant sits on the seat;

[0030] (3) Usually, the definition of the dummy torso angle is equal to the theoretical torso angle; in step 4 of the present invention, the dummy torso angle is adjusted to 25.5-27.5 in order to better simulate the process of a person leaning on the backrest;

[0031] (4) When the finite element model analysis of the seat is usually performed, when the dummy is positioned 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 "the contact between the dummy and the face cover is set separately, and the pressure is output" in order to obtain the maximum pressure, average pressure, contact area, and maximum pressure gradient in the ninth step, so as to evaluate the softness, hardness, stiffness, and comfort design of the seat;

[0032] (5) In the sixth step, an acceleration at an angle of 40 to 50° to the z-direction is loaded to simulate the process of a person sitting on a seat, whereas an acceleration at an angle of 90° to the z-direction is usually loaded. Using an acceleration at an angle of 40 to 50° to the z-direction for loading can more realistically simulate the actual process of a person sitting on a seat.

[0033] In summary, this finite element analysis method is used to simulate and analyze the seat body pressure distribution in a collision. 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

[0034] 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).

[0035] Figure 2 This is an illustration of the model after the dummy positioning is completed.

[0036] Figure 3 The seat deformation diagram and result curve based on the gravity method. DETAILED DESCRIPTION

[0037] The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings:

[0038] A finite element analysis method for seat body pressure distribution based on gravity method comprises the following steps:

[0039] The first step is to establish a finite element model of the entire seat.

[0040] 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;

[0041] 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.

[0042] The second step is to form the prestressed file of the foam and the cover.

[0043] 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.

[0044] 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.

[0045] Step 4: Import the dummy model.

[0046] 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 parts, including the seat headrest, backrest back cover, and seat cushion surface cover.

[0047] The imported dummy model is preferably HIII50, but not limited thereto. The dummy position is adjusted, and the contact between the dummy's feet and the pedal is included, with the pedal being the primary surface and the feet being the secondary surface; the dummy's buttocks and back are 8mm apart 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.

[0048] Step 5: Positioning the dummy.

[0049] The contact between the dummy and the seat components is considered comprehensively during the sitting process, so as to establish contact; the contact between the dummy and the face cover is set separately, and the pressure is output. It is best that the dummy 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.

[0050] Step 6: Load an acceleration that is 40-50° with the z-direction, and gradually adjust the acceleration from 3g to 1g to simulate the process of a person sitting on the seat. Set the card pressure output.intfor. The direction of the acceleration loaded is preferably 45° with the z-direction to simulate the process of a person leaning towards the seat.

[0051] Step 7: Submit dyna calculation; preferably, the calculation is performed using LS-Dyna software.

[0052] Step 8: Read the calculation results, derive the dummy's H point in the calculation results, and compare the H point result with the dummy's theoretical R point. If the coordinates of x, y, and z are within ±10mm, the result is valid; if the coordinate error does not meet the requirements, the loading acceleration needs to be adjusted. This is preferably achieved through Hyperview software.

[0053] Step 9. Read the .intfor result and check the pressure distribution; preferably, this can be done through Hyperview software.

[0054] 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.

[0055] 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;

[0056] 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.

[0057] 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;

[0058] 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 finite element analysis method for seat body pressure distribution based on gravity 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; The contact between the dummy and the seat components during the sitting process is comprehensively considered, so as to establish contact; wherein the contact between the dummy and the face cover is set separately, and the pressure is output; Step 6: Load an acceleration that is 40-50° with the z-axis. Start with 3g acceleration and gradually adjust to 1g acceleration curve to simulate the process of a person sitting on a seat. Set the pressure output on the card.intfor; Step 7: Submit Dyna calculation; Step 8. Read the calculation results, derive the dummy's H point in the calculation results, and compare the H point result with the dummy's theoretical R point. If the coordinates of x, y, and z are controlled within ±10mm, the result is valid; if the coordinate error does not meet the requirements, the loading acceleration needs to be adjusted. 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 finite element analysis method for seat body pressure distribution based on gravity 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 finite element analysis method for seat body pressure distribution based on gravity method according to claim 1, characterized in that: In the fourth step, the imported dummy model is HIII50; the dummy's position is adjusted, 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 finite element analysis method for seat body pressure distribution based on gravity method according to claim 1, 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 finite element analysis method for seat body pressure distribution based on gravity method according to claim 1, characterized in that: In the sixth step, the direction of the loaded acceleration forms a 45° angle with the Z direction to simulate the process of a person leaning towards the seat.

6. The finite element analysis method for seat body pressure distribution based on gravity method according to claim 1, characterized in that: In the seventh step, calculations are performed by LS-Dyna software.

7. The finite element analysis method for seat body pressure distribution based on gravity method according to claim 1, characterized in that: In the eighth step, it is achieved through Hyperview software.

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