Tire simulation method, tire simulation device, and program

Abstract

This allows for improved convergence in convergence calculations while maintaining the accuracy of analytical calculations. [Solution] The tire simulation method includes a tire model creation step S1 for creating a tire model, a rolling analysis calculation step S5 for calculating the sliding speed and contact pressure at each node by performing a rolling analysis using the tire model, a friction coefficient calculation step S6 for determining the friction coefficient at each node, and a friction force calculation step S7 for calculating the friction force at each node. The tire simulation method also includes a friction force correction step S8 for calculating the corrected friction force at a node by determining a correction coefficient to correct the friction force at each node and multiplying the friction force at a node whose sliding speed is within a predetermined range by the correction coefficient, and a tire force calculation step S11 for calculating the tire force, which is the force acting on the tire model, based on the friction force and the corrected friction force. The predetermined range is a range where the lower limit sliding speed is greater than 0 mm / s and the upper limit sliding speed is 390 mm / s or more and 820 mm / s or less.

Description

Technical Field

[0001] The present disclosure relates to a tire simulation method, a tire simulation device, and a program, and particularly relates to a simulation of rolling analysis of a tire.

Background Art

[0002] In recent years, in order to improve the development and design efficiency of pneumatic tires, prediction of tire performance such as frictional force has been performed by numerical analysis using a computer. For example, Patent Document 1 discloses a tire simulation method for setting a value of a friction coefficient between a tire and a road surface by using rubber viscoelastic characteristics in a tire simulation.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a simulation for predicting tire performance, the convergence of the convergence calculation during analysis is an important factor for obtaining the result of the simulation. In the convergence calculation, there are cases where convergence does not occur when it greatly deviates from the actual behavior. In the convergence calculation, for example, when a certain value during the convergence calculation exceeds a threshold value, the analysis calculation is stopped. Particularly, in the rolling analysis where the calculation is complex, the above problem appears显著.

[0005] Against this backdrop, corrections are sometimes made to reduce the force at each node during the analysis in order to improve the convergence of the convergence calculation. However, while making corrections during the convergence calculation improves the convergence of the calculation, there is a problem that the force at the nodes is underestimated as a result of the correction, and the accuracy of the analysis calculation deteriorates. Furthermore, the tire simulation method described in Patent Document 1 cannot solve this problem. [Means for solving the problem]

[0006] The tire simulation method of the present invention includes a tire model creation step of creating a tire model modeled with a finite number of elements having a plurality of nodes; a rolling analysis calculation step of calculating the sliding speed and ground pressure for each node by performing a rolling analysis using the tire model; a friction coefficient calculation step of determining the friction coefficient for each node based on the sliding speed and the ground pressure; and a friction force calculation step of calculating the friction force for each node based on the ground pressure and the friction coefficient, wherein the method includes a friction force correction step of determining a correction coefficient to correct the friction force for each node based on the sliding speed for each node, and calculating the corrected friction force for a node by multiplying the friction force of a node whose sliding speed is within a predetermined range by the correction coefficient; and a tire force calculation step of calculating the tire force, which is a force acting on the tire model, based on the friction force and the corrected friction force, wherein the predetermined range is characterized in that the lower limit of the sliding speed is greater than 0 mm / s and the upper limit of the sliding speed is in the range of 390 mm / s or more and 820 mm / s or less. [Effects of the Invention]

[0007] According to the tire simulation method, tire simulation apparatus, and program of the present invention, by limiting the nodes to be corrected and reducing the number of nodes that are underestimated, it is possible to improve convergence in convergence calculations while maintaining the accuracy of the analytical calculations. [Brief explanation of the drawing]

[0008] [Figure 1]This is a flowchart illustrating the tire simulation method according to the first embodiment. [Figure 2] This diagram shows the relationship between sliding speed and the correction factor. [Figure 3] This figure shows the contact surface of the tire model according to the second embodiment. [Figure 4] This is a block diagram of a tire simulation device. [Figure 5] This figure shows the relationship between the analysis accuracy and the upper limit of the sliding speed within a predetermined range in this embodiment.

[0009] Hereinafter, with reference to the drawings, an example of an embodiment of the tire simulation method, tire simulation apparatus, and program according to the present invention will be described in detail. The embodiments described below are merely examples, and the present invention is not limited to these embodiments. Furthermore, forms obtained by selectively combining the multiple embodiments and modifications described below are included in the present invention.

[0010] Using Figure 1, the simulation method for predicting tire performance according to the first embodiment will be explained in detail. Figure 1 is a flowchart of the tire simulation method according to the first embodiment.

[0011] The tire simulation method according to the first embodiment calculates the tire force acting on the tire model using rolling analysis. The tire simulation method may be performed, for example, using the tire simulation device 1 described later.

[0012] In the tire model creation process, a tire model is created using a finite number of elements, each with multiple nodes (Step S1). Specifically, the dimensional specifications of the tire, such as its external shape and internal structure, as well as the shape, arrangement, and material properties of each tire component, such as the tread rubber, are input.

[0013] In the road surface model creation process, a road surface model is created for rolling the tire model (step S2). In the road surface model creation process, for example, a road surface model having a smooth surface without irregularities is created, but the road surface model may have irregularities. The size of the irregularities may approximate an actual road surface, such as minute irregularities like those on an asphalt road surface, irregular steps, depressions, undulations, or ruts. The road surface model may also be formed on a cylindrical surface, such as that of a drum testing machine.

[0014] In the rolling condition setting process, rolling conditions are set (step S3) as conditions for performing rolling analysis using the tire model created in the tire model creation process. Rolling conditions include conditions on the tire model side, such as rim size and air pressure. Conditions on the road surface model, such as the coefficient of friction, are also set. As will be explained in more detail later, slip ratio and other rolling conditions are set for each cycle of the rolling analysis.

[0015] In the slip ratio setting process, the slip ratio is set as the rolling condition (step S4). In the slip ratio setting process, steps S4 to S9 constitute one cycle, and the slip ratio is changed with each cycle. In the slip ratio setting process, for example, the slip ratio is increased with each cycle.

[0016] In the rolling motion analysis calculation step, the sliding speed and contact pressure at each node are calculated at the slip ratio set in the slip ratio setting step (step S5). Specifically, in the rolling motion analysis calculation step, the sliding speed and contact pressure at each node are calculated by performing a rolling motion analysis using the tire model and road surface model described above. Next, in the friction coefficient calculation step, the friction coefficient at each node is calculated at the slip ratio set in the slip ratio setting step, based on the sliding speed and contact pressure obtained in the rolling motion analysis calculation step (step S6).

[0017] In the frictional force calculation step, based on the ground pressure for each node and the friction coefficient for each node, the frictional force for each node at the slip ratio set in the slip ratio setting step is calculated (step S7). The frictional force calculated in the frictional force calculation step may be stored in a storage medium or the like, linked to each node.

[0018] In the frictional force correction step, a correction coefficient for correcting the frictional force calculated in the frictional force calculation step is obtained for each node of the tire model, and by multiplying the frictional force for each node by the correction coefficient, the corrected frictional force for each node at the slip ratio set in the slip ratio setting step is calculated (step S8). In the frictional force correction step, the corrected frictional force of a node is calculated by multiplying the frictional force of the node whose slip speed is within a predetermined range by the correction coefficient. Here, the predetermined range is a range where the lower limit of the slip speed exceeds 0 mm / s and the upper limit of the slip speed is 390 mm / s or more and 820 mm / s or less. In the frictional force correction step, by correcting the frictional force of the node, the convergence of the convergence calculation can be improved. Also, by limiting the nodes to be corrected, nodes whose frictional force is underestimated due to the correction are limited, and it is possible to suppress the underestimation of the tire force in the entire tire model. That is, while maintaining the accuracy of the tire force obtained by the analysis calculation, the convergence in the convergence calculation can be improved.

[0019] Referring further to FIG. 2, the relationship between the slip speed and the correction coefficient will be described in detail. FIG. 2 is a diagram showing the relationship between the slip speed and the correction coefficient. The dashed line, the one-dot chain line, and the two-dot chain line in FIG. 2 indicate the upper limit of the slip speed in the predetermined range. Specifically, the dashed line indicates a slip speed of 820 mm / s, the one-dot chain line indicates a slip speed of 500 mm / s, and the two-dot chain line indicates a slip speed of 390 mm / s.

[0020] The correction coefficient data illustrated in FIG. 2 is a graph showing the correspondence between the slip speed and the correction coefficient. The correction coefficient shown in the correction coefficient data takes a value greater than 0 and less than or equal to 1. In the frictional force correction step, the slip speed of the nodes of the tire model is acquired, and the correction coefficient corresponding to the slip speed is acquired from the correction coefficient data. The corrected frictional force of the node is calculated by multiplying the acquired correction coefficient by the frictional force of the node.

[0021] The correction coefficient data is data such that the correction coefficient approaches 1 as the slip speed increases, as illustrated in FIG. 2. Specifically, in the correction coefficient data illustrated in FIG. 2, the correction coefficient may be set to 1 at a certain slip speed or higher. Also, in the slip speed range until the correction coefficient becomes 1, the correction coefficient increases logarithmically. According to the above correction coefficient, it is possible to perform correction to reduce the frictional force of each node, particularly the frictional force in the low slip rate region, so that the convergence of the convergence calculation is improved.

[0022] The correction coefficient data may be set based on a predetermined range. Specifically, the correction coefficient data may be set such that the correction coefficient approaches 1 near the slip speed at the upper limit of the predetermined range. For example, when the slip speed at the upper limit of the predetermined range is set to 820 mm / s, correction coefficient data may be set such that the correction coefficient approaches 1 near the slip speed of 820 mm / s, as shown by the solid line in FIG. 2. Also, when the slip speed at the upper limit of the predetermined range is set to 390 mm / s, correction coefficient data may be set such that the correction coefficient approaches 1 near the slip speed of 390 mm / s, as shown by the two-dot chain line in FIG. 2. According to this, it is possible to reliably correct the frictional force of the nodes whose slip speed is within the predetermined range. For example, when the correction coefficient data shown by the two-dot chain line in FIG. 2 is set when the upper limit of the slip speed is 820 mm / s, in the range of 390 mm / s or higher, since the correction coefficient is 1, correction is not substantially performed at the nodes having a slip speed within the range. Therefore, by setting the correction coefficient data based on the slip speed at the upper limit of the predetermined range as described above, it is possible to reliably correct the frictional force of the nodes whose slip speed is within the predetermined range.

[0023] In the friction force correction process, the friction force at each node is corrected using correction coefficient data as shown in Figure 2. For example, if the upper limit of the slip speed is set to 390 mm / s, the correction coefficient is applied only to nodes in the tire model that have a slip speed between 0 mm / s and 390 mm / s or less, and the friction force at those nodes is corrected. Similarly, if the upper limit of the slip speed is set to 820 mm / s, the correction coefficient is applied only to nodes in the tire model that have a slip speed between 0 mm / s and 820 mm / s or less, and the friction force at those nodes is corrected. As will be explained in more detail later, the smaller the upper limit of the slip speed within a given range, the better the analysis accuracy when the slip ratio is 1%. Also, the larger the upper limit of the slip speed within a given range, the wider the range of slip ratios that can be obtained.

[0024] In the convergence determination step, a convergence calculation is performed based on the friction force and corrected friction force at each slip ratio, and a decision is made to continue or interrupt the rolling analysis (step S9). That is, the convergence determination step requires friction force and corrected friction force at at least two slip ratios. In the convergence determination step, if the convergence calculation is convergent (YES in step S9), the rolling analysis is continued and the process proceeds to the next step. In the convergence determination step, if data for friction force and corrected friction force at only one slip ratio is available, a decision is made to continue the rolling analysis.

[0025] In the convergence determination process, as described above, convergence calculations are performed based on the frictional force and corrected frictional force at each node for each slip ratio. Specifically, for nodes where the frictional force has been corrected in the frictional force correction process, the convergence calculation is performed using the corrected frictional force. This improves the convergence accuracy of the convergence calculation. Furthermore, for nodes where the frictional force has not been corrected in the frictional force correction process, the convergence calculation is performed based on the frictional force.

[0026] In the convergence determination step, if the convergence calculation does not converge (NO in step S9), the rolling analysis is stopped and terminated midway, as convergence is deemed impossible. In this case, the analysis is interrupted in an incomplete state, and a solution cannot be obtained. If the convergence calculation converges (YES in step S9), the process proceeds to the next step.

[0027] Next, it is determined whether the slip ratio set in the slip ratio setting step has reached a predetermined value (step S10). If the slip ratio has not reached the predetermined value (NO in step S10), the process returns to the slip ratio setting step, the slip ratio is increased, and the calculations in steps S5 to S9 are performed again. If the slip ratio has reached the predetermined value (YES in step S10), the rolling analysis is terminated, and the process proceeds to the next step.

[0028] The tire force calculation step calculates the tire force acting on the tire model based on the friction force at each node calculated in the friction force calculation step (step S11). The tire force is, for example, the longitudinal force acting along the circumferential direction of the tire model, the lateral force Fy acting along the axial direction of the tire model, and the resultant force of the longitudinal force and the lateral force Fy. The longitudinal force includes the driving force acting in the forward direction of the tire and the braking force Fx acting in the opposite direction to the forward direction of the tire. The braking force Fx is, for example, the sum of the friction forces generated along the direction of travel of the tire model at all nodes. In addition, in the tire force calculation step, the longitudinal load Fz acting in the vertical direction may be calculated from rolling analysis conditions, etc.

[0029] The second embodiment will be described in detail using Figure 3. The first and second embodiments differ in the processing of the friction force correction step. Specifically, in the friction force correction step according to the first embodiment, the friction force of nodes within a predetermined range of sliding speed is corrected, whereas in the friction force correction step according to the second embodiment, the nodes to be corrected are determined by specifying the region within the contact surface between the tire model and the road surface model. Note that the second embodiment is the same as the first embodiment except for the processing of the friction force correction step. Figure 3 is a diagram showing the contact surface between the tire model and the road surface model. Specifically, the region enclosed by the dashed line in Figure 3 shows the contact surface between the tire model and the road surface model.

[0030] Let's explain Figure 3 in detail. As shown above, Figure 3 shows the contact surface between the tire model and the road surface model. More specifically, Figure 3 shows the contact surface of the tire model as seen from the road surface model side. The tire model is formed of a finite number of elements and has nodes connecting the elements. In Figure 3, the rectangles demarcated by lines are elements, and the intersections of the lines are nodes. Also, the vertical direction in Figure 3 is the circumferential direction of the tire model, which is the direction in which the tire model rotates, and the upward direction in Figure 3 is the direction of travel of the tire model. In Figure 3, the areas indicated by dots are the slip regions where the slip velocity exceeds 0 mm / s, and the higher the density of dots, the greater the slip velocity. That is, in the slip regions of Figure 3, the slip velocity increases as you move towards the opposite side of the tire model's direction of travel. Also, the areas within the contact surface that do not have dots are the stuck regions where the slip velocity is 0 mm / s.

[0031] In the friction force correction step according to the second embodiment, as described above, the nodes to be corrected are determined by specifying the region within the contact surface between the tire model and the road surface model. Specifically, as shown in Figure 3, when the circumferential length of the contact surface where the tire model contacts the road surface model is defined as L, the corrected friction force of a node is calculated by multiplying the friction force of the node located within a region L / 4 away from the tire direction of travel side of the slip region where the slip speed exceeds 0 mm / s in the contact surface by a correction coefficient. This makes it possible to correct the friction force of nodes with relatively low slip speeds by specifying the region of the contact surface.

[0032] In Figure 3, the area enclosed by the solid line represents the L / 4 region in the tire model's slip region, extending from the tire's direction of travel side edge to the opposite side of the tire's direction of travel. In the friction force correction step according to the second embodiment, the friction force of the nodes within this region that are located within the slip region is corrected.

[0033] In the friction force correction step according to the second embodiment, similar to the friction force correction step of the first embodiment, a correction coefficient corresponding to the sliding velocity of each node is obtained from the correction coefficient data, and the corrected friction force is calculated by multiplying it by the friction force of each node.

[0034] Furthermore, the tire simulation method described above can be implemented by having a computer execute each step of the tire simulation method as a procedure using a program that executes the tire simulation method.

[0035] The tire simulation device 1 will be described in detail using Figure 4. Figure 4 is a block diagram of the tire simulation device 1 that performs tire performance prediction. The tire simulation device 1 has a configuration that enables the execution of the tire simulation method described above.

[0036] The tire simulation device 1 consists of a computer equipped with a control device 10 including a processor 11 and memory 12, and performs predictive simulations of tire performance. The tire simulation device 1 may consist of one computer or multiple computers. In addition, some of the functions of the tire simulation device 1 may reside on a server or the like connected via a communication network.

[0037] The tire simulation device 1 comprises an input unit 13 and an output unit 14. The input unit 13 is an input interface for inputting information necessary for running the simulation, and examples include a keyboard and a mouse. The information input by the input unit 13 includes, for example, analysis conditions, conditions for creating tire models and road surface models, etc. The output unit 14 is a liquid crystal display, organic EL display, etc., which displays the input screen, the simulation results, and other output screens.

[0038] The tire simulation device 1 has a tire model creation unit 15 that creates a numerically analyzable tire model modeled with a finite number of elements having multiple nodes. The tire model creation unit 15 sets, for example, the shape of the model and the number of mesh divisions. The tire model creation unit 15 creates a tire model based on the information necessary to create a numerically analyzable tire model acquired by the input unit 13, etc. Specifically, it creates a tire model based on various dimensional specifications such as the external shape and internal structure of the tire, material properties such as Young's modulus, Poisson's ratio and specific gravity for each component that makes up the tire, such as the tread, belt and carcass, and various evaluation conditions such as internal pressure and load. This information may be input via a keyboard, a recording medium such as a CD-ROM, or a network.

[0039] In detail, the tire model creation unit 15 uses the tire shape in a natural equilibrium state as the reference shape, models this reference shape using FEM, and creates a three-dimensional tire model that is modeled with a finite number of elements, each having multiple nodes. The finite elements are identified using three-dimensional coordinates (for example, XYZ coordinates where the longitudinal direction of the tire is the X axis, the tire width direction is the Y axis, and the vertical direction is the Z axis). The method of creating such a tire model is publicly known, and it can be modeled using known methods. Alternatively, a previously created tire model may be input from the input unit 13, in which case the tire model creation unit 15 sets the input tire model as the analysis target. As will be described in more detail later, the tire model divided into a finite number of elements has a finite number of nodes located on the boundaries of the finite number of elements and connecting each element. In rolling analysis, the sliding velocity and ground pressure are calculated for each of these nodes.

[0040] The tire simulation device 1 includes a road surface model creation unit 16 that creates a road surface model for rolling the tire model created by the tire model creation unit 15. The road surface model creation unit 16 creates a road surface model having a smooth surface without irregularities, for example, but the road surface model may have irregularities. The size of the irregularities may approximate an actual road surface, such as a micro-irregularity like that of an asphalt road surface, irregular steps, depressions, undulations, or ruts. The road surface model may also be formed on a cylindrical surface, for example, like that of a drum testing machine.

[0041] The tire simulation device 1 has a rolling condition setting unit 17 that sets rolling conditions as conditions for performing rolling analysis of the tire model created by the tire model creation unit 15. Rolling conditions include conditions on the tire model side, such as rim size and air pressure. Conditions on the road surface model, such as the coefficient of friction, are also set. As will be described in more detail later, slip ratio and the like are set as rolling conditions.

[0042] The tire simulation device 1 has a rolling analysis unit 18 that performs rolling analysis based on the tire model and rolling conditions obtained above. The rolling analysis unit 18 has a slip ratio setting unit 19 that sets the slip ratio in the braking analysis. The slip ratio setting unit 19 changes the slip ratio gradually with each calculation cycle as a rolling condition, for example. The slip ratio setting unit 19 sets the road surface speed (vehicle speed V) relative to the tire. V ) and tire rotation speed V T In order to change the slip ratio S determined by the road surface speed (vehicle speed V), V ) and tire rotation speed V T The slip ratio S is given by the following equation (1).

[0043]

number

[0044] In braking analysis, the process starts with a slip ratio of 0%, and the slip ratio setting unit 19 gradually increases the slip ratio at a predetermined rate at each calculation step of the rolling analysis. The rate at which the slip ratio is increased may be constant for each calculation cycle, but it may also be possible to set a larger rate in the initial stages of the rolling analysis and then decrease the rate thereafter to reach the slip ratio at which the target physical quantity is obtained more quickly. It is preferable that the rate at which the slip ratio is increased is constant in order to improve accuracy in the low slip ratio region. For example, the slip ratio setting unit 19 increases the slip ratio by 1% each cycle. For example, the slip ratio setting unit 19 increases the slip ratio by 1% from 0% to 25%.

[0045] The rolling analysis unit 18 includes a rolling analysis calculation unit 20 that performs rolling analysis calculations using the rolling conditions set in the rolling condition setting unit 17 and the slip ratios set in the slip ratio setting unit 19. The rolling analysis calculation unit 20 performs rolling analysis using a tire model and calculates the sliding speed and contact pressure at each node for each slip ratio. After the slip ratio is increased in the slip ratio setting unit 19, the rolling analysis calculation unit 20 calculates the deformation state of the tire model by rolling analysis at that slip ratio. The rolling analysis calculation unit 20 may, for example, associate the calculation results such as the sliding speed and contact pressure at each node with the node number and store them in the memory 12.

[0046] The rolling analysis unit 18 has a friction coefficient calculation unit 21 that calculates the friction coefficient for each node based on the sliding speed and ground pressure obtained by the rolling analysis calculation unit 20. The friction coefficient calculation unit 21 may, for example, pre-set a table showing the relationship between ground pressure, sliding speed and friction coefficient. This table can be pre-set based on analysis calculations and experiments, etc.

[0047] The friction coefficient calculation unit 21 may pre-set a function (specifically, a quadratic function, a higher-order function, an exponential function, a logarithmic function, etc.) in which the ground pressure and sliding speed are independent variables and the friction coefficient is the dependent variable. The friction coefficient calculation unit 21 calculates the friction coefficient from the ground pressure and sliding speed based on this function. This function can be pre-set based on analytical calculations and experiments, etc.

[0048] The rolling analysis unit 18 has a friction force calculation unit 22 that calculates the friction force for each node at each slip ratio based on the ground pressure for each node obtained by the rolling analysis calculation unit 20 and the friction coefficient for each node obtained by the friction coefficient calculation unit 21. Specifically, the friction force calculation unit 22 obtains the friction force for each node by multiplying the vertical force, which is obtained by dividing the ground pressure by the contact area where the node contacts the road surface, by the friction coefficient. The friction force calculation unit 22 may, for example, associate the node number with the friction force of the node with that node number and record it in the memory 12.

[0049] The rolling analysis unit 18 has a friction force correction unit 23 that calculates a correction coefficient for each node based on the sliding speed for each node obtained by the rolling analysis calculation unit 20, and calculates a corrected friction force for each node by multiplying the friction force by the correction coefficient. The friction force correction unit 23 calculates the corrected friction force for a node by multiplying the friction force of a node whose sliding speed is within a predetermined range by the correction coefficient. Here, the predetermined range is a range where the lower limit sliding speed is greater than 0 mm / s and the upper limit sliding speed is between 390 mm / s and 820 mm / s.

[0050] The friction force correction unit 23 can improve the convergence of the convergence calculation by correcting the friction force at the nodes. Furthermore, by limiting the nodes to which the correction is applied, the nodes where the friction force is underestimated due to the correction are limited, thereby suppressing underestimation of the tire force for the entire tire model. In other words, it is possible to improve the convergence of the convergence calculation while maintaining the accuracy of the tire force obtained by the analytical calculation.

[0051] The correction coefficient data is the type of data exemplified in Figure 2. The correction coefficient data exemplified in Figure 2 is a graph showing the correspondence between the sliding speed and the correction coefficient. The correction coefficients shown in the correction coefficient data take values ​​between 0 and 1. The friction force correction unit 23 obtains the sliding speed of the nodes of the tire model and obtains the correction coefficient corresponding to that sliding speed from the correction coefficient data. By multiplying the friction force of the node by the obtained correction coefficient, the corrected friction force of the node is calculated.

[0052] The friction force correction unit 23 corrects the friction force at each node using correction coefficient data as shown in Figure 2. For example, if the upper limit of the sliding speed is set to 390 mm / s, the correction coefficient is applied only to nodes in the tire model that have a sliding speed of 0 mm / s or less than or equal to 390 mm / s, and the friction force at those nodes is corrected. Similarly, if the upper limit of the sliding speed is set to 820 mm / s, the correction coefficient is applied only to nodes in the tire model that have a sliding speed of 0 mm / s or less than or equal to 820 mm / s, and the friction force at those nodes is corrected. As will be explained in more detail later, the smaller the upper limit of the sliding speed within a predetermined range, the better the analysis accuracy when the slip ratio is 1%. Also, the larger the upper limit of the sliding speed within a predetermined range, the wider the range of slip ratio results that can be obtained.

[0053] The rolling analysis unit 18 has a convergence determination unit 24 that performs a convergence calculation based on the friction force and corrected friction force at each slip ratio calculated by the friction force calculation unit 22 and determines whether to continue or interrupt the rolling analysis. The convergence determination unit 24 may, for example, perform the convergence determination based on the sum of the friction force and corrected friction force at all nodes at each slip ratio, or it may perform the convergence determination for each node.

[0054] The convergence determination unit 24 may, for example, determine that convergence is possible and continue the rolling analysis if the difference between the friction force or corrected friction force at each slip ratio is below a predetermined threshold. Alternatively, the convergence determination unit 24 may be configured to determine that convergence is impossible and interrupt the rolling calculation when the difference between the friction force or corrected friction force at each slip ratio exceeds a predetermined threshold. The convergence calculation and convergence determination method in the convergence determination unit 24 are not particularly limited.

[0055] The rolling analysis unit 18 performs the analysis while increasing the slip ratio from 0% until the slip ratio reaches a predetermined value. In other words, the rolling analysis may be terminated when the slip ratio reaches a predetermined value. The predetermined value is, for example, a slip ratio of 100%. In the low slip ratio region, where the slip ratio is low, the tire model has both a slip region where the slip speed exceeds 0 mm / s and a region where the slip speed is 0 mm / s and no slip occurs (a stuck region) at the contact surface between the tire model and the road surface model. This complicates the convergence calculation and increases the possibility of the convergence calculation stopping. Therefore, the friction force correction unit 23 corrects the friction force used in the convergence calculation to be smaller, thereby improving the convergence of the convergence calculation.

[0056] The tire simulation device 1 may include a tire force calculation unit 25 that calculates the tire force acting on the entire tire model based on the results of the rolling analysis unit 18. Specifically, the tire force calculation unit 25 calculates the tire force acting on the tire model using the friction force calculated by the friction force calculation unit 22 and the corrected friction force calculated by the friction force correction unit 23. This limits the number of nodes that are corrected, thereby suppressing underestimation of the tire force and maintaining the accuracy of the analysis calculation.

[0057] Tire forces include, for example, longitudinal forces acting along the circumferential direction of the tire model, lateral forces Fy acting along the axial direction of the tire model, longitudinal loads Fz acting in the vertical direction, and the resultant force of these forces. The longitudinal forces include the driving force acting in the forward direction of the tire and the braking force Fx acting in the opposite direction to the forward direction of the tire. The braking force Fx is, for example, the sum of the friction force and corrective friction force generated along the direction of travel of the tire model at all nodes. The longitudinal load Fz can be obtained from rolling analysis conditions, etc. [Examples]

[0058] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0059] <Example 1> [Creating a tire model] In this example, a numerically analyzable tire model consisting of a finite number of elements with multiple nodes was created based on a tire with a tire size of 215 / 50R17.

[0060] [Rolling Condition Setting] For the rolling motion analysis, a load of 4822N was applied to the axle of the tire model, and the internal pressure was set to 250kPa. In addition, a smooth road surface model was created, and the speed on the road surface (i.e., the vehicle's speed) was set to 60km / h.

[0061] [Rolling analysis] A rolling motion analysis was performed using the finite element method with the above tire model and rolling motion analysis conditions. In this rolling motion analysis, the friction coefficient was calculated from the ground pressure and sliding velocity at each node for each slip ratio, and the frictional force at each node was calculated from the ground pressure and friction coefficient. Furthermore, a correction coefficient was determined according to the sliding velocity at each node, and the corrected frictional force at a node was calculated by multiplying the frictional force at a node within a predetermined sliding velocity range by the correction coefficient determined according to the sliding velocity. In Example 1, the predetermined range is the range where the lower limit sliding velocity exceeds 0 mm / s and the upper limit sliding velocity is 750 mm / s or less. The convergence of the rolling motion analysis was determined based on the frictional force at the uncorrected nodes and the corrected frictional force at the corrected nodes. The slip ratio was increased by 1% increments from 0% to 25% during the rolling motion analysis.

[0062] [Tire force calculation] After determining the convergence of the rolling motion analysis, the braking force Fx acting on the tire model was calculated based on the friction force and corrected friction force obtained from the rolling motion analysis. Here, the braking force Fx was calculated by summing the friction force and corrected friction force acting in the opposite direction to the tire's direction of travel at all nodes. In addition, the longitudinal load Fz acting vertically downward on the axle of the tire model was calculated from the rolling motion analysis conditions.

[0063] <Example 2> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 500 mm / s.

[0064] <Example 3> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 450 mm / s.

[0065] <Example 4> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 435 mm / s.

[0066] <Example 5> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the specified range was set to 420 mm / s.

[0067] <Example 6> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 400 mm / s.

[0068] <Example 7> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 390 mm / s.

[0069] <Comparative Example 1> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 380 mm / s.

[0070] <Comparative Example 2> The simulation was performed in the same manner as in Example 1, except that the upper limit of the sliding speed within the predetermined range was set to 1500 mm / s.

[0071] [Evaluation of acquired data points] Table 1 shows the analysis results for Examples 1-7 and Comparative Examples 1 and 2. In Examples 1-7 and Comparative Examples 1 and 2, the analysis was performed by increasing the slip ratio from 0% to 25% in 1% increments. As a result, data such as friction force was obtained at each node of the tire model for each slip ratio. That is, since the slip ratio usually changes from 0% to 25% at each node, 26 data points are obtained.

[0072] [Evaluation of the ratio of braking force Fx to longitudinal load Fz (Fx / Fy)] Table 1 and Figure 5 show the analysis results for Examples 1-7 and Comparative Examples 1 and 2. In these examples, the braking force coefficient μ, obtained by dividing the braking force Fx by the longitudinal load Fz, is used to compare the examples and comparative examples. Table 1 shows the number of data points acquired and the error rate of the values ​​for the examples and comparative examples relative to the measured values ​​when the slip ratio is 1%. Comparative Example 1 is not applicable because data could not be acquired. The braking force coefficient μ when the slip ratio is 1% is called braking stiffness and is an important indicator that mainly shows the characteristics of the initial braking effect during braking. The measured braking force coefficient μ is determined experimentally. In the experiment, the braking force Fx and longitudinal load Fz were measured under the same conditions as in the above analysis calculation, and the braking force coefficient μ was determined.

[0073] [Table 1]

[0074] In Figure 5, the vertical axis represents the error rate of the braking force coefficient μ, and the horizontal axis represents the upper limit of the sliding speed. In Figure 5, the results for Examples 1 to 7 are shown with black circles, and the results for Comparative Example 2 are shown with white circles. Comparative Example 1 is not shown because the number of acquired data points was 0. In addition, Figure 5 shows the approximate straight line obtained by performing linear regression based on each data point. The equation that shows this approximate straight line is given by equation (2) below.

[0075]

number

[0076] In equation (2), y represents the error rate of the braking force coefficient μ, which is the vertical axis in Figure 5, and x represents the sliding speed, which is the horizontal axis in Figure 5.

[0077] As shown in Table 1, it can be confirmed that Examples 1 to 7 were able to obtain data for each slip ratio compared to Comparative Example 1. In detail, the larger the upper limit of the predetermined slip speed, the more data was obtained. Since the slip ratio is increased in increments of 1% from 0%, for example, in Example 7, data was obtained at four points for slip ratios of 0%, 1%, 2%, and 3%. Furthermore, if data is obtained at even one point where the slip ratio exceeds 0%, the simulation of the braking force of the tire model is valid. Therefore, it is preferable that the upper limit of the predetermined slip speed is 390 mm / s or higher. That is, if the upper limit of the predetermined slip speed is 390 mm / s or higher, data can be obtained by rolling analysis.

[0078] As shown in Figure 5, it can be confirmed that the error between the measured value of the braking force coefficient μ and the values ​​of the examples 1 to 7 (black dots in Figure 5) is smaller compared to Comparative Example 2. In other words, it can be confirmed that the analytical calculation accuracy is improved in Examples 1 to 7 compared to Comparative Example 2. Furthermore, it can be confirmed that the error between the measured value and the values ​​of the examples decreases as the upper limit of the sliding speed within the predetermined range decreases. Note that for analytical accuracy, the error rate between the measured value of the braking force coefficient μ and the values ​​of the examples must be 15% or less. Therefore, we substitute 15 for y in equation (2) and find x. As a result, it can be confirmed that it is preferable for the upper limit of the sliding speed within the predetermined range to be 820 mm / s or less. In other words, if the upper limit of the sliding speed within the predetermined range is 820 mm / s or less, the accuracy of the analytical calculation can be maintained. In conjunction with the above results, it is preferable for the upper limit of the sliding speed within the predetermined range to be 390 mm / s or more and 820 mm / s or less. In other words, the predetermined range is preferably one in which the lower limit of the sliding speed exceeds 0 mm / s and the upper limit of the sliding speed is between 390 mm / s and 820 mm / s. By correcting the frictional force at nodes within the sliding speed range described above, it is possible to improve convergence in the convergence calculation while maintaining the accuracy of the analytical calculation. [Explanation of symbols]

[0079] 1 Simulation device, 10 Control device, 11 Processor, 12 Memory, 13 Input unit, 14 Output unit, 15 Tire model creation unit, 16 Road surface model creation process, 17 Rolling condition setting unit, 18 Rolling analysis unit, 19 Slip ratio setting unit, 20 Rolling analysis calculation unit, 21 Friction coefficient calculation unit, 22 Friction force calculation unit, 23 Friction force correction unit, 24 Convergence determination unit, 25 Tire force calculation unit

Claims

1. A tire model creation process involves creating a tire model using a finite number of elements with multiple nodes, A rolling analysis calculation process is performed using the aforementioned tire model to calculate the sliding velocity and contact pressure at each node, A friction coefficient calculation step in which the friction coefficient for each node is determined based on the sliding speed and the ground pressure, A friction force calculation step that calculates the friction force at each node based on the ground pressure and the coefficient of friction, A tire simulation method including, A friction force correction step involves determining a correction coefficient to correct the friction force for each node based on the sliding velocity for each node, and calculating the corrected friction force for a node by multiplying the friction force of a node whose sliding velocity is within a predetermined range by the correction coefficient. The process includes a tire force calculation step that calculates the tire force, which is the force acting on the tire model, based on the friction force and the corrected friction force, A tire simulation method in which the predetermined range is such that the lower limit of the slip speed exceeds 0 mm / s and the upper limit of the slip speed is in the range of 390 mm / s or more and 820 mm / s or less.

2. The tire simulation method according to claim 1, wherein the tire force is a longitudinal force acting along the circumferential direction of the tire model, a lateral force acting along the axial direction of the tire model, and the resultant force of the longitudinal force and the lateral force.

3. The tire simulation method according to claim 1, further comprising a convergence determination step of performing a convergence calculation based on the corrected friction force and determining whether to continue or interrupt the rolling analysis.

4. The tire simulation method according to claim 1, wherein the correction coefficient takes a value between 0 and 1, and becomes closer to 1 as the slip speed increases.

5. A tire model creation process involves creating a tire model using a finite number of elements with multiple nodes, A road surface model creation step for creating a road surface model for rolling the aforementioned tire model, A rolling analysis calculation process is performed using the aforementioned tire model to calculate the sliding velocity and contact pressure at each node, A friction coefficient calculation step in which the friction coefficient for each node is determined based on the sliding speed and the ground pressure, A friction force calculation step that calculates the friction force at each node based on the ground pressure and the coefficient of friction, A tire simulation method including, A friction force correction step is performed by determining a correction coefficient for correcting the friction force at each node based on the sliding velocity at each node, defining the tire circumferential length of the contact surface where the tire model contacts the road surface model as L, and multiplying the friction force at a node located within a region L / 4 on the opposite side of the tire direction of travel from the tire direction side end of the sliding region where the sliding velocity is greater than 0 on the contact surface by the correction coefficient to calculate the corrected friction force at that node. A tire force calculation step that calculates the tire force, which is the force acting on the tire model, based on the friction force and the corrected friction force, A tire simulation method, including the following.

6. A program for causing a computer to execute the tire simulation method described in any one of claims 1 to 5.

7. A tire model creation unit that creates a tire model using a finite number of elements having multiple nodes, A rolling analysis calculation unit calculates the sliding velocity and contact pressure at each node by performing a rolling analysis using the aforementioned tire model. A friction coefficient calculation unit that determines the friction coefficient for each node based on the aforementioned sliding speed and the aforementioned ground pressure, A friction force calculation unit calculates the friction force at each node based on the ground pressure and the coefficient of friction, A tire simulation device comprising, A friction force correction unit calculates a correction coefficient for correcting the friction force at each node based on the sliding speed at each node, and calculates the corrected friction force at a node by multiplying the friction force at a node whose sliding speed is within a predetermined range by the correction coefficient. The system includes a tire force calculation unit that calculates the tire force, which is the force acting on the tire model, based on the friction force and the corrected friction force, The predetermined range is a tire simulation device in which the lower limit of the slip speed exceeds 0 mm / s and the upper limit of the slip speed is in the range of 390 mm / s or more and 820 mm / s or less.

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