JP2003191729A - Method for travel simulation for tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conduct travel simulation on a snowy road or the like with high precision. <P>SOLUTION: This method includes: a step S1 for setting a tire model in which a tire is modeled using an element allowing numerical analysis; a step S2 for setting a road surface forming subject model in which a road surface forming subject is modeled using an element allowing numerical analysis and allowing an expression of a volume change by compression; and a simulation step S4-S8 for conducting the travel simulation of the tire by imparting a condition where the tire model contacts with the road surface forming subject model and rotates, and by conducting deformation calculation for the tire model and the road surface forming subject model in every very small time increment. The simulation step includes correction processing for correcting a calculated stress based on a preliminarily set characteristic curve indicating a stress and a volume strain in plastic deformation, when the road surface forming subject model is judged to be under the plastic deformation and a load-applied condition. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simulating a tire running on a compressible road surface formation whose volume changes by being compressed, such as snow and soil.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
For tire development, we made a prototype and actually tested it.
It was a repetitive work of making further prototypes from the experimental results. However, this method has a limit in improving the development efficiency because it requires a lot of cost and time for manufacturing the prototype and the experiment. In order to overcome such problems,
In recent years, there has been proposed a method of predicting / analyzing performance to some extent by computer simulation using a numerical analysis method such as a finite element method, without making a tire.

However, the conventional proposals are limited to a simulation in which a tire is run on a paved road surface or a road surface where a water film exists. Water is generally treated as an incompressible perfect fluid in analytical models. On the other hand, in a concrete simulation in the case where a tire runs on a road surface covered with a road surface forming material such as snow and soil, which is hardened by compression and hardened and whose volume change is permanent, the above-mentioned conventional proposal is I can't respond. Therefore, for example, in order to improve the snow running performance of tires,
After all, many real vehicle tests are required. In particular, since it is difficult to artificially create a snow road, it can be tested only during a limited snow cover period, which causes a large development cost and development period for this type of tire.

As a result of earnest studies, the inventors of the present invention have conducted a simulation by examining the deformation state when a compressible road surface formation such as snow and soil is compacted by a tire, separately for elastic deformation and plastic deformation. It was found that the calculation time can be greatly shortened by accurately capturing the stress and correcting the stress during plastic deformation based on a predetermined characteristic curve. Then, the inventors have found that, for example, it is possible to accurately simulate running on a snowy road with tires, and eventually to investigate the interaction between the tires and the road surface formation, thus completing the present invention. As described above, an object of the present invention is to provide a tire simulation method capable of efficiently simulating a state of running on a road surface structure having compressibility with a tire in a relatively short calculation time.

[0005]

According to a first aspect of the present invention, there is provided a step of setting a tire model in which a tire is modeled by a numerically analyzable element, and a numerical change capable of numerical analysis and a volume change due to compression. The step of setting a road surface formation model that models a road surface formation with an element that can express, and a condition for the tire model to contact and roll with the road surface formation model, and to deform the tire model and the road surface formation model. A simulation step of performing a traveling simulation of the tire by performing calculation for each minute time increment, and the simulation step includes a road surface forming object based on a volume strain of a road surface forming object model and a predetermined volume elastic modulus. Deformation determination process for determining the stress of the model and determining whether the deformation of the road surface formation model is plastic deformation or elastic deformation A load determination process for determining whether the road surface formation model is in a load-loaded state or a load-unloaded state, and when it is determined that the road surface formation model is in a plastically deformed and load-loaded state, the road surface formation model A traveling simulation method for a tire, comprising: a correction process of correcting the calculated stress based on a characteristic curve indicating a relationship between a stress and a volume strain during a plastic deformation set in advance.

The invention according to claim 2 is characterized in that the correction processing corrects the calculated stress to a stress corresponding to the volume strain of the road surface formation model determined from the characteristic curve. The tire traveling simulation method according to Item 1.

According to a third aspect of the present invention, in the load determination processing, whether the road surface formation model is in a load-loaded state or a load-unloaded state is based on the positive or negative sign of the strain rate of the road surface formation model. 3. The tire traveling simulation method according to claim 1, wherein

In the invention according to claim 4, the characteristic curve is an approximation obtained by approximating a stress-volume strain curve obtained from a compression test result of a road surface formation by one or more of a spline curve, a plurality of straight lines or a logarithmic curve. The tire traveling simulation method according to any one of claims 1 to 3, wherein the method comprises a curved line.

According to a fifth aspect of the present invention, in the simulation step, the position, shape and speed of the tire model are given as boundary conditions when calculating the deformation of the road surface formation model, and the shape and speed of the road surface formation model are given. And the reaction force is given as a boundary condition when calculating the deformation of the tire model.

The invention according to claim 6 is characterized in that the road surface forming object is snow, and the road surface forming object model is a snow model, and the running simulation of the tire according to any one of claims 1 to 5. Is the way.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings by taking a snow running simulation in which snow is used as a compressible road surface formation and a tire runs on the snow. FIG. 1 shows a computer device 1 for carrying out the simulation method of the present invention.
The computer device 1 includes a main body 1a, a keyboard 1b and a mouse 1c as input means, and a display device 1d as output means. Body 1a
Although not shown in the figure, an arithmetic processing unit (CPU), R
OM, working memory, large-capacity storage device such as a magnetic disk, and storage devices such as CD-ROM and flexible disk drives 1a1 and 1a2 are appropriately provided. The mass storage device stores a processing procedure (program) for executing a simulation method described later.

FIG. 2 shows an example of the processing procedure of the simulation method of the present invention, which will be described below in order.
First, in this embodiment, a tire model in which a tire is modeled by an element that can be numerically analyzed is set (step S
1). The numerical analysis is possible means that it can be handled by a numerical analysis method such as a finite element method, a finite volume method, a difference method, or a boundary element method. In this example, the finite element method is adopted.

FIG. 3 is a three-dimensional visualization of an example of the tire model 2. The tire model 2 includes a finite number of small elements 2a, 2
Numerical data that can be handled by the computer device 1 is obtained by modeling by dividing into b, 2c, .... Specifically, the nodal coordinate values, shapes, and material properties of the elements 2a, 2b, 2c ... Are defined, for example, density, Young's modulus, damping coefficient and the like. Each element 2 is not particularly limited.
For a, 2b, 2c ..., For example, a quadrilateral element as a two-dimensional plane and a three-dimensional element are preferably tetrahedral solid elements suitable for expressing a complicated shape. However, other than this, a pentahedral solid element, a hexahedral solid element, or the like can be used, and any element that can be processed by a computer is used.

A three-dimensional solid element is preferably used mainly for the rubber portion constituting the tire. In Fig. 3, the pattern shape including the vertical and horizontal grooves on the tread surface is faithfully reproduced, but if you want to focus on studies other than patterns, simplify or omit the tread groove from the tread surface. It can also be a smooth model. Note that the circumferential length of one element is 25% of the contact length so that the distribution of pressure and shearing force at the tread contact part can be expressed.
It is desirable that the length be less than or equal to 20 mm, and the length of one element in the axial direction of the tire be less than or equal to 20 mm so that an arc in the cross-sectional direction of the tread can be smoothly expressed.

Further, as shown in FIG. 4, the tire model 2 may be provided with a detailed pattern portion Ai that faithfully models the tread surface and a simplified pattern portion Bi that simplifies the tread surface. . Although the detailed pattern portion Ai is defined in a range larger than the contact length, it is useful to reduce the total number of elements of the tire model and shorten the calculation time by making the area smaller than the simple pattern portion Bi. Moreover, it is desirable to set various conditions so that the simulation result can be obtained when the detailed pattern portion Ai contacts the snow model.

As shown in FIG. 5, the composite material constituting the tire, such as the belt ply and the carcass ply, has the cord array c coated on the quadrilateral membrane elements 5a and 5b and the cord array. The topping rubber t is modeled in each of the solid elements 5c to 5e, and these are modeled as a composite shell element 5 in which these are sequentially laminated in the thickness direction. In the quadrilateral membrane element, a thickness equal to the diameter of the cord c1 and anisotropy of different rigidity in the arrangement direction of the cord c1 and the direction orthogonal to this are defined. Further, each solid element dividing the rubber can be defined and handled as, for example, a super viscoelastic material. It should be noted that such a tire model 2 first specifies a two-dimensional shape in a meridional section including the rotation axis of the tire and rotates it in the circumferential direction around the virtual tire rotation axis to obtain a unit of a predetermined circumferential length. Modeling can also be performed relatively easily by dividing the elements into elements. 3D CAD
It is also possible to accurately divide by using the data of.

Next, in this embodiment, a process of setting a snow model (road surface formation model) modeling snow is performed (step S2). Similar to the tire model 2, the snow model is modeled so that it can be numerically analyzed and can express the volume change due to compression.

FIG. 6 shows the relationship between the snow volume obtained by the experiment and the compressive force (hydrostatic pressure compressive stress) acting on the snow. As indicated by the solid line in the figure, as the compressive force on snow increases, its volume decreases. Further, in the initial stage of compression, the volume changes substantially linearly, and has an elastic deformation region A in which the stress and the volume strain are substantially proportional to each other. The proportional constant between the volume strain and the stress in the elastic deformation region A is defined as the volume elastic modulus.
Further, when a compressive force is applied beyond the elastic deformation region A to compress it to, for example, X1, and then unloading is performed, the volume is restored with an inclination parallel to the bulk elastic modulus as shown by a chain line. Then, the elastic strain is recovered and the plastic strain remains. That is, the volume change due to compression is permanent (plastic deformation region B). Three chain lines are shown in the figure, but all are parallel to the slope of the bulk modulus.

In the present embodiment, such snow is modeled by, for example, a hexahedral Euler element that can be handled by the finite volume method. FIG. 7 shows a road surface model 8 having a snow model 6.
And a side view of the snow model 6 is illustrated in FIG. 8A. The snow model 6 is equivalent to snow, for example, which is filled with a lattice-shaped mesh 6a fixed in a space above the plane rigid element 7 and a cubic space 6b partitioned by the mesh 6a and whose characteristics are defined in FIG. Virtual filling 6c
Composed of and. The thickness H of the filler 6c corresponds to the snow thickness of the snow road to be analyzed. Further, the snow model 6 is given the width and length required for rolling of the tire model 2.
Further, the snow model 6 may be defined in a state of being in contact with the tire model 2 from the beginning, or may be defined after being separated from each other and then contacted. When the snow model 6 is used as an Euler element, it is possible to avoid problems such as the collapse of the mesh and the negative volume of the element when the deformation of the material becomes large, compared to the case where the Lagrange element suitable for the structure is used. However, it is preferable. However, the snow model is not limited to Euler elements.

As shown by hatching in FIG. 8B, for example, when the snow model 6 and the tread block 9 of the tire model 2 come into contact with each other, the tread block 9 is located in the deformation calculation of the snow model 6. The filler 6c representing the snow on the part is pushed away, and as shown in FIG.
c remains. Then, the removed filler 6c is calculated as compressed in each cubic space. The volumetric strain of snow is calculated for each element by comparing the volume of the filling 6c in each cubic space 6b before and after the time increment (calculation step) for calculating the deformation of the snow model 6 as described later. You can Then, the compressive force to one element is sequentially transmitted to other adjacent elements, and a series of deformation states can be simulated.

Further, as shown in FIG. 9, one cubic space 6b of the snow model 6 has a volume V1 of 100% thereof in the initial state.
The filler 6c corresponding to (= L1 × L2 × L3) snow is filled, but when the surface 9A of the tread block of the tire model 2 enters this cubic space, the volume V2 of the changed filler 6c is It becomes {(L1-L4) * L2 * L3}. Then, the volume ratio of the filling material 6c before and after the change (V2 / V
According to 1), the volume strain of the filling material 6c (that is, snow) can be calculated. The volumetric strain is the sum of the elastic volumetric strain that is restored to the original after unloading and the plastic volumetric strain in which the strain remains after unloading, but as shown by the chain line in FIG. Defined as very small. And the filling 6
When the structure is removed, c holds the plastic volume strain as shown in FIG. 8 (C). As a result, the snow model 6
Can express the volume change due to compression.

The plane rigid element 7 is defined with a rigid body characteristic such that the surface is not deformed. In this example, the plane rigid element 7 restricts the inflow / outflow of the filler 6c from the bottom surface Se5 of the snow model 6. Further, with respect to the left and right side surfaces Se1 and Se2, the front side surface Se3, and the rear side surface (not shown) of the snow model 6, it is possible to give conditions for prohibiting the inflow and outflow of the filler 6c from the outside. Various settings can be made according to the condition of the road surface. Between the other meshes 6a, the filling material 6c can be set to flow in and out. Further, the road surface model 8 can be formed by omitting the planar rigid element 7 by setting conditions for prohibiting the inflow / outflow of the filler 6c on the bottom surface Se5 of the snow model 6.

In the present embodiment, as shown in FIG. 10, a characteristic curve L indicating the relationship between stress and volume strain during plastic deformation of the snow model 6 is stored in the storage device in advance as a function or numerical data. Has been done. As the characteristic curve L, for example, an approximate curve that approximately expresses a stress-volume strain curve that can be calculated from the result of the snow compression test (FIG. 6) is used.

The characteristic curve L of this embodiment is defined from the elastic deformation region A to the plastic deformation region B. In the elastic deformation area A, the volumetric strain of the snow model 6 and the stress (hydrostatic stress) are proportional to each other, and the relationship between the two is defined by one straight line L1. Further, in the plastic deformation region B, as shown in FIG. 6, the stress and volume (that is, volume strain) of the snow model 6 form a curved line that cannot be represented by one straight line. In this example, the relationship between the stress and the volume strain in the plastic deformation region B is approximated to the experimental result of FIG. 6 by using a polygonal line connecting a plurality of straight lines L2 to L5 having different inclinations. The slopes of the straight lines L2 to L5 (that is, the slopes having the bulk elastic modulus in the elastic region) are all smaller than the bulk elastic modulus of the elastic deformation region A, and the plastic deformation region B has a small compressive stress in the snow model. It expresses that it transforms.

The characteristic curve L is obtained by connecting a plurality of straight lines to approximate the experimental result. For example, as shown in FIG. 11A, the coordinates of the plurality of control points P1, P2 ... It can be approximated by using a spline curve LS in which the control points are smoothly interpolated based on, or a logarithmic curve La as shown in FIG. 11 (B).
Note that FIG. 11B illustrates an example in which the characteristic curve L is formed by combining the logarithmic curve La and the straight line L1.
It can also be defined by combining various curves and the like.

Next, in this embodiment, boundary conditions and the like are set (step S3). The conditions to be set include, for example, the rim assembly condition of the tire model 2, the internal pressure filling condition, the friction coefficient between the snow model 6 and the tire model 2 (that is, the friction between the tire model 2 and the snow model 6 is The tire model 2 and the snow model 6 may be included in the initial time increment when the deformation of the snow model 6 is calculated, the bulk elastic modulus of the snow model 6, and the like.

In order to apply the rim assembly condition to the tire model 2, for example, as shown in FIG. 12, the width W of the bead portion of the tire model 2 is set by restraining the rim contact areas b, b of the tire model 2. The forced displacement is made equal to the rim width, and the rotation axis CL of the virtual tire model 2 and the constraint area b
The tire radial distance r between and is always set equal to the rim diameter. Further, in order to set the internal pressure filling condition in the tire model 2, a uniformly distributed load ω corresponding to the tire internal pressure is applied to the inner surface of the tire model 2 on the tire bore side.

Further, in this example, the explicit method is adopted for the simulation calculation. In the explicit method, the moment when a load or the like acts on each model is set to time 0 without performing a convergence calculation, the time is divided at each set time increment, and the displacement of the model at each time is obtained. And this time increment is
It is desirable to set so as to satisfy the Courant condition for stable calculation. Specifically, the initial time increment Δt during the deformation calculation of the tire model 2 and the snow model 6 is set to a value that satisfies the following formula. Δt <Lmin / C

Here, Lmin is a representative length of the smallest element among the elements constituting each model, and C is the transmission velocity of the stress wave propagating in the structure, which can be obtained by √ (Ei / ρi). (Ei: Young's modulus, ρi: mass density). By thus setting the time increment so as to satisfy the Courant condition, as shown in FIG. 13, for example, when the external force F acts on the element e1, the external force F is adjacent to the element e1.
It is possible to calculate the deformation state e1 ′ of the element e1 before it is transferred to 2.

Further, in the present embodiment, the stress wave propagation time is calculated from the size and density of the element based on the above formula, and in this example, the minimum value of the stress wave propagation time is multiplied by the safety factor to determine the initial time. Increment is set. Therefore, the optimum deformation calculation can be performed for all the elements. It is desirable that the safety factor is, for example, 0.8 or more and less than 1.0. This initial time increment is specifically 0.1 to 5 μsec for the tire model 2 and the snow model 6, respectively.
, More preferably 0.3 to 3 μsec, and further preferably 0.5 to 2 μsec.

Next, in the present embodiment, conditions for the tire model to come into contact with the snow model 6 (road surface forming object model) and roll are given, and deformation calculation of the tire model 2 and the snow model 6 (road surface forming object model) is performed. The tire running simulation is performed by performing the above-mentioned time increments (steps S4, S).
5). The conditions may include, for example, a shaft load condition acting on the tire model 2, a slip angle during rolling, a camber angle, and / or a traveling speed. Then, in this example, a predetermined speed (translational speed, rotational speed) is applied to the tire model 2 that comes into contact with the snow model 6 to roll on the snow model 6.

As is apparent from steps S4 to S8 in FIG. 2, the tire model 2 is used in this embodiment.
And the deformation calculation of the snow model 6 are separately performed. Then, the shape and velocity data of the tire model 2 obtained by the deformation calculation of the tire model 2 are given as boundary conditions at the time of the deformation calculation of the snow model 6 (step S8), and also obtained by the deformation calculation of the snow model 6. An example is shown in which the shape, speed, and reaction force are given as boundary conditions when the deformation of the tire model 2 is calculated (step S7). So-called "coupling". The details will be described below.

FIG. 14 shows an example of a specific processing procedure for the deformation calculation of the tire model 2. For the deformation calculation of the tire model 2, first, the deformation calculation after the time increment Δt is performed (step S41). In this example, the finite element method is used for the deformation calculation, and the equation of motion shown by the following equation is used.

[Equation 1]

Next, in this embodiment, the stress wave propagation time is recalculated based on the size and density of each element of the deformed tire model 2 (step S42).
In this example, the time increment calculated from the minimum value of the stress wave propagation time is set as the next time increment (step S4).
3). The stress wave propagation time depends on the size of the element,
Since it is a function of density, it changes with each element deformation. This example includes a step of calculating an optimum time increment each time according to the deformation state of the element, so that more accurate deformation calculation of the tire model 2 can be performed, which is useful for obtaining a highly accurate simulation result. .

Next, it is checked whether or not the time designated in advance (defined) has elapsed (step S44). If not, the process returns to step S41, and the newly calculated time increment is added. Then repeat the calculation. When the predetermined time has elapsed (Y in step S4), the deformation calculation of the tire model 2 is completed and the process returns to step S6.

FIG. 15 shows an example of a concrete processing procedure of the deformation calculation of the snow model 6. First, in step S51,
Stress calculation is performed for each element of the snow model 6 after the time increment. For the stress calculation, the predetermined bulk modulus k and
Based on the volume strain ε of the element of the snow model 6, the stress P acting on each element is calculated from the following equation. The volume strain of the element can be calculated from the position of the surface 9A of the tread block of the tire model 2 as shown in FIG. The information on the position of the surface 9A of the tread block is obtained by the snow model 6 by a process (step S8 in FIG. 2) described later.
Given to the side.

[Equation 2]

Next, load determination processing is performed to determine whether the deformation of the elements of the snow model 6 is in a load-loaded state or a load-unloaded state (step S52). Here, the loaded state is
It is a relative load state (compression only, not considering tension) when the deformation state of the element obtained in the previous calculation step is used as a reference, and the unloading state is obtained in the previous calculation step. Relative unloading state (non-compressed state) based on the element deformation state.

This load judgment processing can be judged by checking the positive and negative signs of the strain rate for the elements of the snow model 6, for example. Strain rate is the strain divided by the time required for the deformation. The magnitude of the strain rate represents the speed of deformation of the element, and the sign of the strain rate indicates, for example, that the strain is tensile strain when it is positive and that it is compressive strain when it is negative. And
In the determination of this example, when the strain rate is negative, it is determined as the load applied state in which the relative compressive strain acts. In this way, the strain rate is calculated from the deformation state of the element obtained in the previous calculation step and the deformation state of the element in the current calculation step, and the sign thereof is checked to obtain the element of the present snow model 6. It is possible to determine whether or not is a loaded state or an unloaded state.

Next, when it is judged that the load is applied (step S52), the current deformation state of the element is the elastic deformation area A.
Or in the plastic deformation region B (step S54). For example, as shown in FIG. 10, on the coordinates of the characteristic curve L, the calculated deformation state of the element (stress,
Plot the volumetric strain). Since this deformed state uses the bulk modulus, the straight line L1 or the extended line L must be used.
Located on 1 '. If it is in the elastic deformation region A like the plot point Ya, it is judged to be elastic deformation, and the plot point Yb
When it is in the plastic deformation region B as described above, it can be judged as plastic deformation. Various judgment methods can be adopted, and it is also possible to examine the magnitude of distortion and the like. Also, Drucker-Prager
It is also possible to use the yield conditions of Then, when the deformation of the element is determined as the plastic deformation (step S5)
3), the stress of the element of the snow model calculated in step S51 is corrected to the stress based on the characteristic curve L (step S54).

In step S51, assuming that the element is elastically deformed, the volume strain ε and the volume elastic modulus K are calculated.
The stress is calculated using and. Therefore, when the actual stress state of the element is plastic deformation, it is considered that the element is deformed with a smaller stress. In other words, it is necessary to reduce the stress. Therefore, in the present embodiment, step S52
When both the step S54 and the step S54 are satisfied, the characteristic curve L is corrected to a stress corresponding to the volume strain. Specifically, when the deformation state obtained by the calculation is, for example, the point Yb in FIG. 10, the volume stress εb is corrected to the maximum stress value Yb ′ on the characteristic curve.

When simulating the deformation of an object,
Since elastic deformation is proportional to stress and strain, simulation can be performed relatively easily. However, as in the present example, in a snow simulation in which most of the deformation is plastic deformation, it is not easy to obtain the stress during plastic deformation of the snow model as a stable solution in a short time. Therefore, in the present invention, when the deformation of the snow model is determined to be a load-loaded state and plastic deformation, the stress is pulled back to the maximum value on the predetermined characteristic curve that the element can actually bear (stress). By easing the), the stress is sought immediately, albeit in a pseudo manner, and the calculation time is greatly shortened and a stable simulation is realized.

When the element of the snow model 6 is in the unloading state (N in step S52) or the deformation is elastic deformation (N in step S53), the stress state obtained in step S51 is adopted as it is. can do.

Next, in this embodiment, as in the case of the tire model 2, the stress wave propagation time is recalculated for each element of the deformed snow model 6, and in this example, the stress wave propagation time is minimized. The value is set as the next time increment (step S55).

Next, it is checked whether or not the time designated in advance (defined) has elapsed (step S56). If it has not elapsed, the process returns to step S51, and the time increment is newly calculated again. Calculate. When the predetermined time has elapsed (Y in step S56), the deformation calculation of the snow model 6 is completed, and the process returns to step S6.

In steps S7 and S8, the two models are coupled to each other by passing necessary data to each other based on the deformation calculation results of the tire model 2 and the snow model 6 which are calculated separately and independently. For example, next tire model 2
In the deformation calculation step of, the shape of the snow model 6,
Velocity and pressure data (stress data) are given as conditions. The stress data acts as a reaction force on the tread block surface of the tire model 2. On the other hand, the shape of the tire model 2 (position information on the tread block surface 9A) and the speed are given as conditions for the next deformation calculation of the snow model 6. Note that this coupling is performed in the state of the tire model 2 and the snow model 6 at the same time.

Therefore, the tire model 2 is included in the snow model 6.
A new change in compressive strain and stress due to a change in the rotation position can be reproduced, while the deformation of the tire model 2 is reproduced by the reaction force received from the snow model 6.
Then, by repeating such calculation, the tire model 2 and the snow model 6 are taken into consideration while considering not only the compression characteristics of snow but also the interaction between the tire model 2 and the snow model 6.
It is possible to couple and calculate the deformation states that change from moment to moment. In step S6, it is determined whether or not a predetermined time for completing the calculation has elapsed, and if Y is determined in step S6, the calculation result is output (step S6).
9), the process ends. Tire model 2 and snow model 6
The coupling with (steps S7 to S8) is set so that both models have the same time. The time for finishing the calculation in step S6 can be variously set so that a stable calculation result can be obtained according to the simulation to be executed.

Further, in the present invention, the stress of the element at the time of plastic deformation of the snow model 6 is derived by a very simple process of correcting the stress obtained on the premise of elastic deformation based on a predetermined characteristic curve L. You can As a result, for example, as stress calculation during plastic deformation, no convergence calculation by repeated loop processing is required, and the calculation time can be greatly reduced.

Various information can be included in the output of the calculation result. For example, when a driving force (or a braking force) is applied to the tire model 2, the front-rear direction force transmitted to the snow model 6 at that time is extracted to evaluate the tire driving performance (or braking performance) on a snow road. , Help to improve. When the tire model 2 is run on a snow model with a slip angle, the lateral force generated in the tire model 2 is output, so that the cornering performance of the tire on snow can be evaluated and analyzed. The information to be output is not limited to these values, and various kinds of information can be output as necessary.

Based on these output results, the necessary tire internal structure, profile change, pattern improvement, rubber material improvement, etc. are performed, and the shape, depth, thickness, etc. of the siping are changed. It is possible to actually make a prototype of a tire for which a suitable simulation result is obtained. As a result, for example, the development period of a winter tire can be significantly shortened and the development cost can be reduced. And
It is possible to manufacture a tire with good results by performing evaluations on an actual vehicle for the prototype tire. If the actual vehicle evaluation does not match the simulation result, it is desirable to make a modification to reflect this result in the simulation software.

FIG. 16 shows an example of visualizing the traveling simulation of the present invention. A rut 10 generated when the tire model 2 travels is formed in the snow model.

FIG. 17 shows the relationship between the longitudinal force of the tire model, the radial force and time in the snow running simulation. The simulation shows that stable driving force and reaction force are obtained from about 0.04 seconds after the start after running.

Although the present invention has been described above, the tire model 2 is run on the fixed snow model 6 in the above embodiment. On the contrary, the rotation axis of the tire model 2 is only freely rotated. By allowing the snow model 6 to be in contact with the tire model 2 while allowing it to be fixed, the rolling state of the tire model can be reproduced by the frictional force. In this case, it is possible to set a fixed length for the snow model 6 and to add snow models sequentially from the front edge thereof and delete the snow model from the rear edge thereof.

Further, in the above embodiment, the snow model is modeled by the Euler element. However, the snow model may be modeled by a Lagrangian element which is generally used for modeling a structure. Conventionally, it has been considered that when a large deformation occurs, the Lagrangian element cannot be calculated due to element destruction such as the element becoming a negative volume as shown in FIGS. 18 (A) to 18 (B). However, when a large amount of deformation occurs, for example, as shown in FIG. 18C, by considering that the contact between the side of the element and the node does not occur, the element is further deformed into, for example, a film shape, and the adjacent It is possible to reproduce the characteristics of snow even with the Lagrangian element by defining the element so that only the force is transmitted.

Differences in snow quality, such as solid snow, dry snow, compressed snow, and fresh snow, include, for example, bulk elastic modulus of snow model elements,
It can be generally expressed by changing the friction coefficient and the like. Further, in the above-described embodiment, snow has been described as an example of the road surface forming object, but soil or the like which is a compressible material can also be adopted as the road surface forming object. When modeling soil, if the bulk modulus of the element is set differently from snow, the others can be defined substantially the same as snow.

[0055]

As described above, according to the driving simulation method of the present invention, the running performance on snow, for example, can be roughly known without actually making a trial tire.
Therefore, the tire development period and cost can be reduced. Further, in the simulation method of the present invention, for example, the stress obtained by the calculation of the elements of the snow model indicates the relationship between the stress and the volume strain at the time of preset plastic deformation during load and plastic deformation. It is modified based on the characteristic curve. Therefore, it is possible to calculate the stress at the time of plastic deformation, which is difficult to stabilize, in a short time, and it is possible to shorten the simulation time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a computer device for implementing a simulation method of the present invention.

FIG. 2 is a flowchart showing an example of a processing procedure of a simulation method of the present invention.

FIG. 3 is a perspective view of a tire model of the present invention.

FIG. 4 is a side view of a tire model showing another embodiment of the present invention.

FIG. 5 is a conceptual diagram showing element modeling of a cord reinforcing material.

FIG. 6 is a graph showing the relationship between the compressive force of snow and the volume.

FIG. 7 is a perspective view of a snow model.

FIGS. 8A to 8C are diagrams illustrating a snow model.

FIG. 9 is a diagram illustrating compression of a snow model.

FIG. 10 shows an example of a characteristic curve of a snow model.

11A and 11B show other examples of characteristic curves.

FIG. 12 is a cross-sectional view illustrating a rim assembly condition of a tire model.

FIG. 13 is a perspective view of an element.

FIG. 14 is a flowchart showing a specific example of tire model deformation calculation.

FIG. 15 is a flowchart showing a specific example of snow model deformation calculation.

FIG. 16 is a diagram showing a visualized traveling simulation.

FIG. 17 is a graph showing the results of a traveling simulation.

18 (A) to (C) are diagrams illustrating a Lagrangian element.

[Explanation of symbols]

2 tire model 6 snow model

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akio Miyoro             3-6-9 Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo               Sumitomo Rubber Industries, Ltd.

Claims (6)

[Claims] 1. A step of setting a tire model in which a tire is modeled by a numerically analyzable element, and a road surface former modeled by a numerically analyzable element capable of expressing a volume change due to compression. A step of setting a model and conditions for the tire model to contact and roll on the road surface formation model are given, and the tire running simulation is performed by calculating the deformation of the tire model and the road surface formation model at every minute time increment. Along with including a simulation step to perform, the simulation step, the process of calculating the stress of the road surface formation model based on the volume strain and a predetermined bulk modulus, the deformation of the road surface formation model is plastic deformation or elasticity. Deformation determination processing to determine whether it is deformation, and to determine whether the road surface formation model is in a loaded or unloaded state Load determination process, when the road surface formation model is determined to be in plastic deformation and load state, the calculated stress of the road surface formation model, the stress and the volume strain during preset plastic deformation And a correction process for making a correction based on a characteristic curve indicating the relationship between the two. 2. The correction process calculates the calculated stress by
The tire traveling simulation method according to claim 1, wherein the stress is corrected to a stress corresponding to the volumetric strain of the road surface formation model determined from the characteristic curve. 3. The load determining process determines whether the road surface formation model is in a load-loaded state or a load unloading state based on a positive or negative sign of a strain rate of the road surface formation model. The traveling simulation method for a tire according to claim 1 or 2. 4. The characteristic curve is a stress-volume strain curve obtained from a compression test result of a road surface formation, a spline curve,
4. The tire traveling simulation method according to claim 1, comprising an approximation curve that is approximated by one or more of a plurality of straight lines or logarithmic curves. 5. The simulation step provides the position, shape and velocity of the tire model as boundary conditions when calculating the deformation of the road surface formation model, and the shape, velocity and reaction force of the road surface formation model of the tire model. The boundary condition is given when the deformation is calculated.
5. The tire traveling simulation method according to any one of 4 to 4. 6. The road surface formation object is snow, and the road surface formation object model is a snow model.
5. A tire traveling simulation method according to any one of 1.