JP4943709B2 - Pneumatic tire design method - Google Patents

Description

  The present invention relates to a method for designing a pneumatic tire, and in particular, can efficiently and easily design and develop the structure and shape of the tire, and can design the tire while obtaining the best structure and shape of the tire. The present invention relates to a pneumatic tire design method.

To evaluate tire performance at the time of tire design, we actually designed and manufactured the tire and attached it to the actual vehicle, so we evaluated the case where performance was not expected, then redesigned and manufactured it, and attached it to the actual vehicle. Re-evaluated performance. However, recently, to reduce the time, the performance of tires can be predicted with the development of numerical analysis methods such as the finite element method and computer (computer) environment. By the way, in the tire design, the internal pressure state of the tire and the load state on the tire are related to the contact pressure distribution on the contact surface between the tire and the road surface, and uneven wear tends to occur if the contact pressure distribution is uneven, It affects the stability of driving and tire wear performance. For example, even if the design is performed with a standard load and the contact pressure is not biased, if the tire contact pressure is biased between the shoulder and the center during heavy loads, uneven wear may occur and adversely affect the handling stability. Sometimes. For this reason, a technique is known in which a tire is modeled according to the state of the tire and the tire is designed using a numerical analysis method by a computer (see Patent Document 1). With this technique, a tire can be designed in consideration of one state, such as an internal pressure state of the tire and a load state on the tire. In addition, as another tire design, a technique for designing a tire in consideration of a contact pressure distribution is also known (see Patent Document 2).
International Publication No. WO94 / 16877 JP 2000-052716 A

  However, the use condition in which the tire is used is not necessarily a single state such as an internal pressure state of the tire or a load on the tire (hereinafter referred to as tire load). Therefore, if a tire is designed in consideration of any one state, the tire performance may not be exhibited in other states. For example, when designing the external shape of a pneumatic tire, it is preferable to consider the ground contact characteristics of the tire under the use conditions in which the tire is used. However, even in the case of tires of the same size, the internal pressure state and load state of the tire during use vary depending on the mounting shaft (front shaft, rear shaft, etc.) to the vehicle. It also varies depending on the load variation due to the number of passengers in the vehicle and the cargo load. It is preferable to design a tire in consideration of these use conditions.

  In view of the above facts, an object of the present invention is to provide a method for designing a tire shape that exhibits good tire performance in accordance with tire use conditions.

In order to achieve the above object, a pneumatic tire design method according to the present invention includes (a) a tire basic model representing a tire cross-sectional shape including an internal structure, and a tire use state including at least one of tire internal pressure and load A plurality of use conditions representing the tire, and for each of the plurality of use conditions, as a physical quantity for tire performance evaluation, a distribution of contact pressure at the time of a heavy load and an objective function representing a contact area at the time of a light load are determined, and the tire cross-sectional shape or Defining a design variable that determines the tire structure, and a constraint condition that restricts at least one of a tire cross-sectional shape, a tire structure, a physical quantity for performance evaluation, and a tire size; and (b) the use in consideration of the constraint condition Find the values of the design variables that give values that are better than the initial value of the objective function for multiple objective functions, and that all objective function values for each condition are within the allowable range. And step includes that consisting of the step of designing the tire based on the design variable which gives the optimum value of (c) the objective function.

  In step (a) of the present invention, a tire basic model is determined, a plurality of usage conditions are input, an objective function is determined thereafter, and design variables and constraint conditions are determined. This tire basic model represents a tire cross-sectional shape including an internal structure. The tire basic model is for analysis divided into a plurality of elements. Other examples of the tire basic model may include various lines representing a belt, a carcass, a carcass ply folding line, and various reinforcing material lines inside the tire. Further, a plurality of use conditions to be input represents a use state including at least one of a tire internal pressure and a load assumed when the tire is used. An objective function representing a physical quantity for tire performance evaluation is determined for each of the plurality of input usage conditions. As this objective function, tire ground contact characteristics or the like can be used. The ground characteristics include, for example, a tire ground shape, a ground pressure, a ground area and the like. At the same time, design variables that determine the tire cross-sectional shape or tire structure are determined. As this design variable, a function representing the tire outer surface shape or the like can be used as an example representing the tire outer surface shape or the tire structure. Next, a constraint condition that restricts at least one of the tire cross-sectional shape, the tire structure, the physical quantity for performance evaluation, and the tire size is determined. As an example of this constraint condition, there are the circumference of the outer shape of the tread, the tread thickness, the contact length, the contact width, the tire size, and the like. Note that the objective function, the design variable, and the constraint condition are not limited to the above example, and various ones can be determined according to the tire design purpose.

  Next, in step (b), design variables that improve the values of all objective functions for each of the plurality of input usage conditions while satisfying all the constraints for the plurality of input usage conditions. Find the value. As an optimization method using a multi-objective function, a satisfaction trade-off method, a multi-objective genetic algorithm, or the like can be used. When it is impossible to improve all the objective functions, it is possible to improve the objective functions with high priority and determine whether other objective functions with low priority are within a predetermined allowable range. As an example.

  In the next step (c), the tire is designed by changing the tire basic model based on the design variable obtained in step (b). Thus, it is possible to design a tire in consideration of a plurality of use conditions.

The method for designing a pneumatic tire according to claim 2 includes: (a) defining a tire basic model representing a tire cross-sectional shape including an internal structure, and indicating a use state of the tire including at least one of a tire internal pressure and a load. A plurality of conditions are input, and a tire function evaluation physical quantity for each of the plurality of use conditions is determined as an objective function representing a ground contact characteristic at a heavy load indicating a riding state and a ground contact characteristic at a small load indicating an empty state, and a tire. A step of determining a design variable that determines a cross-sectional shape or a tire structure, and a constraint condition that constrains at least one of the tire cross-sectional shape, the tire structure, a physical quantity for performance evaluation, and a tire size; (b) while considering the constraint condition All values of the objective function for each use condition are within a predetermined allowable range, and a value that is improved from the initial value of the objective function is given to a plurality of objective functions. And (c) designing a tire based on the design variable obtained in step (b).

  When the tire is used, the ground contact characteristics also vary depending on the use condition of the tire, which affects the tire performance. Therefore, it is preferable in consideration of grounding characteristics under a plurality of use conditions. Therefore, the objective function, which is a physical quantity for tire performance evaluation, is defined as the grounding characteristic, and the grounding characteristic for each usage condition is expressed as a physical quantity, so that all the usage conditions are satisfied while considering the grounding characteristics for each usage condition. Optimization is possible, and tire design with good ground contact characteristics is possible even under all use conditions.

  A third aspect of the present invention is the pneumatic tire designing method according to the second aspect, wherein the objective function represents a relationship between a tire load and a tire ground contact characteristic, and the design variable is a tire outer shape. It is characterized by that.

  As described above, when the objective function is set in consideration of the ground contact characteristics of the tire, other use conditions may be affected. For example, the ground contact characteristics of the tire may vary depending on the tire load. Therefore, in the present invention, an objective function representing the relationship between both the tire load and the tire ground contact characteristic is adopted. Thereby, the ground contact characteristics of the tire including the tire load can be taken into consideration. At the same time, the present invention adopts the tire external shape as a design variable. The ground contact characteristics of the tire are greatly influenced by the location where the tire comes into contact with an article (for example, a road surface) other than the tire. Therefore, by adopting the tire external shape as the design variable, it is possible to easily design the tire in consideration of the tire load and the tire ground contact characteristics. As an example, the objective function is set so that the bias of the contact pressure is minimized when the load is large and the contact area is maximized when the load is small. A predetermined evaluation is performed on the objective function, and a design variable that gives the best value of these objective functions is obtained. As this predetermined evaluation, in addition to the satisfaction trade-off method, multi-objective genetic algorithm, etc., an integrated objective function that is weighted and added to the objective function for each usage condition is set, or the objective function for each usage condition is set. On the other hand, for example, a threshold value is determined in advance for each use condition, and a value that allows all objective functions to fall within the range of the threshold value is used as an example. As a result, when using the tire, it is possible to design a tire capable of sufficiently exerting tire performance with respect to a plurality of use conditions in which a ground contact area is large at a small load and a ground pressure bias is small at a heavy load.

  A fourth aspect of the present invention is the pneumatic tire designing method according to the third aspect, wherein the tire outer shape is an outer contour shape of a tire tread portion.

  The location where the tire outer shape contributes to the ground contact characteristics is mainly the tire tread portion. For this reason, by setting the outer contour shape of the tire tread part as a design variable and optimizing the objective function representing the ground contact characteristics while considering the constraint conditions, the processing load is larger than when the entire tire outer shape is targeted. It is reduced.

  A fifth aspect of the present invention is the pneumatic tire designing method according to the third aspect, wherein the tire outer shape is an outermost peripheral portion of a tire tread portion in a tire radial direction.

  The portion where the tire tread portion contributes to the ground contact characteristic is mainly the outermost peripheral portion in the tire radial direction of the pattern portion, that is, the tire tread portion. Therefore, the processing load can be further reduced by optimizing the objective function representing the ground contact characteristics while considering the constraint conditions with the outermost peripheral portion of the tire tread portion in the tire radial direction as a design variable.

  Invention of Claim 6 is a pneumatic tire design method of any one of Claim 3 thru | or 5, Comprising: The relationship between the said tire load and a ground contact characteristic is a tire position in a vehicle, It is characterized by considering a vehicle condition indicating either the cargo load amount or the number of passengers in the vehicle.

  The tire load and ground contact characteristics vary depending on the position of the tire in the vehicle, the cargo load, and the number of passengers in the vehicle. For this reason, even if it is the same tire, tire performance will differ with vehicle conditions. Therefore, the use conditions (the internal pressure state and the load state of the tire) corresponding to the position of the tire in the vehicle, the cargo load amount, and the number of passengers in the vehicle are obtained, and the tire design is performed in consideration of all the use conditions. The same can be said for the occurrence of toe angles and camber angles, which are tire angles in vehicles, so it is also possible to design tires by obtaining usage conditions according to tire toe angle and camber angle. is there. As a result, it is possible to design a tire capable of obtaining good performance depending on vehicle conditions.

  As described above, according to the present invention, since a plurality of use conditions of a tire including at least one of internal pressure and load are set and optimized in consideration of all the use conditions, an excellent tire under a plurality of use conditions There is an effect that a tire that exhibits performance can be designed.

  Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an outline of a personal computer for carrying out the pneumatic tire designing method of the present invention. The personal computer includes a keyboard 10 for inputting data and the like, a computer main body 12 that performs arithmetic processing to determine the tire shape in accordance with a program stored in advance, and a CRT 14 that displays the arithmetic results of the computer main body 12 and the like. It is composed of

  Next, an embodiment for designing the outer shape of the tire in order to improve the tire performance will be described. In the present embodiment, the unevenness of the ground pressure distribution in the contact area at the time of a heavy load is minimized, and the ground contact area at the time of a small load is maximized.

FIG. 2 shows a processing routine of the program of this embodiment. FIG. 3 shows an example of the tire cross-sectional shape, and the tire tread portion TR, the tire belt BL, and the carcass CS are shown as representative portions. In step 100, the tire cross-sectional shape of FIG. 3 is used as a reference shape, and this reference shape is modeled by a technique capable of numerically and analytically determining tire ground contact characteristics, such as a finite element method, and includes a tire including an internal structure. A tire basic model that represents a cross-sectional shape and is divided into a plurality of elements by mesh division is obtained. Here, modeling means that the tire shape, structure, material, and pattern are digitized into an input data format to a computer program created based on a numerical / analytical method. FIG. 5 shows the tire basic model. FIG. 5 shows a carcass line CL, a line OL representing the tire outer surface shape, a folded ply line PL, or a line representing the belts B1 and B2. This tire basic model is divided into a plurality of elements by a plurality of normals NL ₁ , NL ₂ , NL ₃ ,... Of a line OL representing the tire outer surface shape. In the above description, an example in which the tire basic model is divided into a plurality of elements by a plurality of normals of the line representing the outer shape of the tire has been described, but a plurality of normals of the carcass line and a plurality of normals of the folded ply line May be divided into a plurality of elements, or may be divided into arbitrary shapes such as a triangle according to the design purpose.

In step 102, the values of the load and the internal pressure are input as tire use conditions M _t (1 ≦ t ≦ n, where n is the total number of use conditions). For this input, a value input by the user using a keyboard or the like may be read, or a predetermined value may be read from the memory. The use conditions include a predetermined combination of internal pressure and load that is predicted to be mainly used for tires. In this case, a plurality of use conditions of a large load and a small load are input as the load. In the case of a load, it is conceivable to input a load value, but an input value corresponding to the application may be used. As an example of the input value according to the usage, there are the number of passengers and cargo loading. In the case of the number of passengers, a predetermined standard weight is stored, and the load value can be obtained by multiplying the input number of persons by the standard weight and a predetermined coefficient. In addition, a standard number of passengers other than the driver may be experimentally obtained in advance, and an input value representing an empty state and a boarding state may be used. In this case, the distribution of the load on the tire may be different depending on the distribution of the boarding positions of the passengers on the vehicle. Therefore, a position where the tire is mounted on the vehicle, for example, front shaft mounting or rear shaft mounting may be specified (input), or the left and right positions may be specified (input). Further, as another use condition, a camber angle, a toe angle, or the like can be used in consideration of a difference in vehicle alignment. In the next step 104, an objective function representing a physical quantity for tire performance evaluation is defined for each of a plurality of use conditions input in 102, and a constraint condition for restricting the tire cross-sectional shape and a design variable for determining the tire cross-sectional shape are determined. In the embodiment, an objective function OBJ _t (1 ≦ t ≦ n, where n is the total number of use conditions) is designed to design a tire having tire performance that improves steering stability performance even under each of a plurality of use conditions. And the constraint condition G _t (1 ≦ t ≦ n, where n is the total number of use conditions) is defined as follows.

Objective function OBJ: Ground pressure distribution under heavy load,
Ground contact area under small load Constraint G: Ground pressure bias is within a predetermined value or ground contact area is within a predetermined value. Further, as an example, the tire outer surface shape as a design variable is a Lagrange of FIG. Determined by interpolation routine. In step 130 of this Lagrangian interpolation routine, a reference point P is set inside the tire as shown in FIG. In the next step 132, the range of the node q ₁ of the center of the line representing the tire outer contour the nodal point q ₂ in the vicinity to be bound to the rim, to specify a range of changing the tire shape. Since the location that contributes to the ground contact characteristics is the tire tread portion, in order to reduce the processing load, the range from the node q _{1 at} the center of the line representing the tire outer surface shape to the node q ₃ near the end of the tire tread portion, You may specify as a range which changes a tire shape. In step 134, a straight line connecting the node q ₁ and the reference point P is used as a reference line, and a prospective angle θ that is an angle formed by the reference line and a straight line connecting the node q ₂ and the reference point P is calculated. At 136, the angle increment dθ is calculated according to the following equation:

dθ = θ / degree of Lagrange interpolation (1)
The order of Lagrange interpolation is input in advance by the user.

In step 138, as shown in FIG. 6, imaginary lines L ₁ , L ₂ , L ₃ ,... Are assumed for each angle increment dθ with reference to the reference line, and normals nl ₁ , nl closest to the imaginary line are assumed. ₂ , nl ₃ ,... In the next step 140, as shown in FIG. 7, the outermost nodes Q ₁ , Q ₂ , Q ₃ ,... On the selected normal lines nl ₁ , nl ₂ , nl ₃ ,. The distances r ₁ , r ₂ , r ₃ ,... With the point P (hereinafter expressed as r _{i in the} general formula, where i = 1, 2,... Lagrange interpolation order-1), the node Q ₁ , Q ₂ , Q ₃ ,... Prospective angles θ ₁ , θ ₂ , θ ₃ ,... (Hereinafter expressed as θ _{i in the} general formula. However, i = 1, 2,. The order −1) is calculated. In step 142, the distance r _i is set as a design variable.

After determining a plurality of objective functions OBJ _t, constraint conditions G _t , and design variables r _i for each use condition M _t in this way, in step 106 of FIG. 2, the initial value r of the design variable r _i for each use condition. the initial value OBJ _o of the objective function OBJ _t in _o, as well as calculating the _t, and calculates the initial value G _{0, t} constraints _{G t.}

In the next step 108, to each changed by [Delta] r _i design variables r _i in order to change the tire basic model. In step 110, the distance r _m between the outermost node and the reference point P other than the node Q _i outermost corresponding to the design variable is calculated by the following equation. However, θ _m is a prospective angle from the reference line of the straight line connecting the node and the reference point P.

In this step 110, nodes other than the outermost node on the normal line (nodes on the tire outer surface shape), that is, the nodes CL on the line CL representing the carcass line, the folded ply line PL, and the lines B1 and B2 representing the belt. obtains distances between the node Q _i outermost and obtains the node coordinates other than the outermost nodes on normal by adding the distance obtained in the coordinates of the node Q _i outermost, [Delta] r _i change the design variable The tire cross-sectional shape after being made, that is, the tire correction model is determined.

In step 112, the objective function value OBJ _{i, t} and constraint value G _{i, t} for each use condition M _t after changing the design variable Δr _i for the tire correction model obtained in step 110 are calculated. As a result, the value of the objective function and the constraint condition for each of the plurality of use conditions M _t is obtained. According In step 114 the following equation (3), determine the sensitivity Dobj / dr of the objective function is the ratio of the amount of change of the objective function for each use condition M _t for unit variation of a design variable and determined for each design variable. At the same time, the sensitivity dG / dr of the constraint condition, which is the ratio of the change amount of the constraint condition to the unit change amount of the design variable, is determined for each use condition M _t and for each design variable.

This sensitivity can be predicted whether the value of the use conditions values and constraints of the objective function for each M _t is the extent to which changes when brought into [Delta] r _i changed design variables. Note that this sensitivity may be obtained analytically depending on the method used for tire modeling and the nature of the design variables, and in this case, the calculation in step 112 is not necessary.

  In the next step 116, using the initial value of the objective function, the initial value of the constraint condition, the initial value of the design variable, and the sensitivity, the amount of change in the design variable that optimizes the objective function while satisfying the constraint condition by mathematical programming. Predict. Here, as described above, the objective function or the like is determined for each use condition, and its value is also calculated. For this reason, in step 116, it is necessary to consider a plurality of objective functions and the like simultaneously. Therefore, each objective function is maximized while satisfying each constraint condition by mathematical programming using the initial value of the objective function for each use condition, the initial value and sensitivity of the constraint condition, and the initial value of the design variable. Alternatively, the amount of change in the design variable to be minimized is predicted. As a result, the amount of change in the design variable that optimizes all objective functions can be obtained as a predicted value.

In step 118, a tire correction model is determined by the same method as in step 110, and an objective function value is obtained for each use condition. In the next step 120, the difference between the objective function value OBJ _{i, t} obtained in step 118 and the initial value OBJ _{o, t} of the objective function obtained in step 106 is calculated for each use condition. It is determined whether or not the value of the objective function has converged by determining whether or not each of the calculation results is included in a threshold value range that is input in advance for each use condition. If it is determined that the value of the objective function has not converged, steps 106 to 120 are repeatedly executed with the design variable obtained in step 116 as an initial value. On the other hand, if it is determined that the objective function has converged, the shape of the tire is determined in step 122 with the value of the design variable at this time. Note that the determination in step 120 may continue to be denied without being affirmed. In this case, the determination can be affirmed a certain number of times.

  As described above, in the present embodiment, the tire external shape is optimized in consideration of each of a plurality of use conditions, so that a tire capable of exhibiting tire performance under those use conditions can be designed. In other words, as an example of the objective function, the contact pressure distribution at the time of heavy load and the ground contact area at the time of light load are adopted, and by optimizing the tire shape, the ground area at the time of light load is increased while the ground contact area at the time of light load is increased. It is possible to design a tire with tire performance having good ground contact characteristics at a plurality of load levels in which pressure deviation is suppressed to a minimum.

  Next, examples of the present invention will be described. In this example, tire performance based on a tire model designed by a conventional optimization method and tire performance based on a tire model designed according to the above-described embodiment are respectively obtained and compared.

  The tire modeled as this example employs a light truck winter tire 7.00-16. In this type of tire, if the contact area decreases when the load is small, the snow / ice road performance will be inferior when the load is small, and uneven wear will occur if the contact pressure of the shoulder increases compared to the center when the load is large. It is known to occur. Tires designed by conventional optimization methods, if the main point is to keep the shoulder contact pressure under heavy loads low, the outer contour of the crown will be expressed as a small arc. The ground contact area becomes smaller. On the other hand, if the main point is to increase the ground contact area under small loads, the outer contour of the crown will be represented by a large arc. In this case, the shoulder ground pressure during heavy loads will increase and wear will occur. Performance will deteriorate. On the other hand, as described above, in the embodiment of the present invention, each tire performance under a plurality of use conditions is improved.

  In this embodiment, in the above-described light truck winter tire, an internal pressure of 600 KPa is applied, a small load (3 KN) and a large load (7.0 KN) are set, and the ground contact area, shoulder ground pressure and center ground pressure are obtained. The results of determining the ratio of shoulder ground pressure / center ground pressure are shown in Table 1. In Table 1, calculation is performed using an index when the result of the conventional method is set to 100. FIG. 8 shows the calculation results of the ground contact area as an image. Thereby, the result of Table 1 and FIG. 8 was obtained.

  As understood from Table 1 above, the tire external shape is optimized in consideration of a plurality of internal pressure / load conditions, so that a tire design that maintains good tire performance even under different internal pressure / load conditions is possible. By manufacturing a tire based on the tire design, a high-performance tire can be provided even under a plurality of use conditions.

It is the schematic of the personal computer used for the Example of this invention. It is a flowchart which shows the processing routine of 1st Example of this invention. It is a diagram showing a tire basic model. It is a processing routine which determines the design variable of FIG. It is the diagram which divided the tire basic model into meshes. FIG. 6 is a diagram showing a state in which a virtual line passing through a reference point P is drawn for each dθ on the tire basic model of FIG. 5. FIG. 6 is a diagram showing the relationship between a selected node Q _i , a distance r _i for this node, a prospective angle θ _{i, and the} like. It is the figure which calculated | required the ground contact characteristic using FEM calculation with respect to the tire model calculated | required from implementation of this invention.

Explanation of symbols

10 Keyboard 12 Computer body 14 CRT

Claims (6)

A pneumatic tire design method including the following steps.
(A) A tire basic model representing a tire cross-sectional shape including an internal structure is defined, a plurality of use conditions representing a use state of a tire including at least one of a tire internal pressure and a load are input, and tire performance evaluation is performed for each of the plurality of use conditions. Defines the objective function that expresses the distribution of contact pressure under heavy loads and the contact area under light loads as physical quantities for use , and design variables that determine tire cross-sectional shape or structure, tire cross-sectional shape, tire structure, and performance evaluation Defining a constraint that constrains at least one of a physical quantity and tire size.
(B) A design in which the values of all the objective functions for each use condition are within a predetermined allowable range while considering the constraint conditions, and give a value that is improved from the initial value of the objective function for a plurality of objective functions. The step of obtaining the value of the variable.
(C) A step of designing a tire based on the design variable obtained in the step (b). A pneumatic tire design method including the following steps .
(A) A tire basic model representing a tire cross-sectional shape including an internal structure is defined, a plurality of use conditions representing a use state of a tire including at least one of a tire internal pressure and a load are input, and tire performance evaluation is performed for each of the plurality of use conditions. As a physical quantity, the objective function representing the ground contact characteristic at the time of heavy load indicating the riding state and the ground contact characteristic at the time of light load indicating the empty state is determined, and the design variable for determining the tire cross-sectional shape or tire structure, the tire cross-sectional shape, Defining a constraint condition that restricts at least one of a tire structure, a physical quantity for performance evaluation, and a tire size.
(B) A design in which the values of all the objective functions for each use condition are within a predetermined allowable range while considering the constraint conditions, and give a value that is improved from the initial value of the objective function for a plurality of objective functions. The step of obtaining the value of the variable.
(C) A step of designing a tire based on the design variable obtained in the step (b).   3. The pneumatic tire design method according to claim 2, wherein the objective function represents a relationship between a tire load and tire contact characteristics, and the design variable is a tire outer shape.   The method for designing a pneumatic tire according to claim 3, wherein the outer shape of the tire is an outer contour shape of a tire tread portion.   The method for designing a pneumatic tire according to claim 3, wherein the outer shape of the tire is an outermost peripheral portion in a tire radial direction of a tire tread portion.   The relationship between the tire load and the ground contact characteristic takes into account a vehicle condition indicating any one of a tire position in the vehicle, a cargo load amount, and a number of passengers in the vehicle. A method for designing a pneumatic tire according to claim 1.