JP7576445B2 - A method for evaluating tires to obtain parameters that can be used for tire design. - Google Patents

Description

The present invention relates to a tire evaluation method for obtaining parameters that can be used in tire design.

Traditionally, tires have been designed to improve braking performance. For example, Patent Document 1 proposes using tire characteristics related to the braking performance of a tire as an objective function, determining design parameters that optimize the objective function, and designing a tire using the determined design parameters.

JP 2005-8011 A

However, because braking performance is an important aspect of a tire, there was a need to design a tire that could further improve braking performance.

The present invention aims to provide a tire evaluation method that can be used to design tires with good braking performance.

A tire evaluation method according to an embodiment includes a step of obtaining a plurality of tire models having different parameters, and for each of the plurality of tire models, a step of dividing a tread portion of the tire model into a plurality of portions, a step of contacting the tire model with a road surface model and analyzing its behavior using a finite element method, a step of determining a relationship between slip rate and friction coefficient for each portion based on the results of the behavior analysis, and determining a peak μ slip rate, which is the slip rate when the friction coefficient is maximum in each portion, a step of determining a variation in the peak μ slip rate for each portion, and a step of identifying a tire model having a minimum variation in the peak μ slip rate from among the plurality of tire models .

The tire evaluation method of the embodiment can determine the variation in peak μ slip rate for each part in multiple tire models, and can be used to design tires with good braking performance.

FIG. 3 is a flowchart of a tire evaluation method. FIG. 2 is a perspective view of a finite element model of a tire. A diagram showing the adhesive and slippery areas of a tire. FIG. 13 is a diagram showing the results of integrating the relationship between braking force and slip ratio for each part and each area. FIG.

The embodiment will be described with reference to the drawings. Note that the embodiment is merely one example of the present invention, and any appropriate modifications that do not deviate from the spirit of the present invention are considered to be within the scope of the present invention.

Figure 1 shows a tire evaluation device 10 that performs the tire evaluation method of this embodiment. The tire evaluation device 10 includes a tire model acquisition unit 11 that acquires a tire model, which is a model of a pneumatic tire; a road surface model acquisition unit 12 that acquires a road surface model; a part setting unit 13 that divides the contact surface of the acquired tire model into a plurality of parts; a boundary condition setting unit 14 that sets boundary conditions for tire behavior analysis; a behavior analysis unit 15 that performs tire behavior analysis; a classification unit 16 that classifies the nodes of the tire model into adhesion regions or slippage regions; an integration unit 17 that integrates the physical quantities of the nodes obtained by the behavior analysis by the behavior analysis unit 15 for each part and for each region; a μ-S diagram creation unit 18 that creates a μ-S diagram for each part and determines the peak μ slip rate for each part, which will be described later; a μ-S diagram analysis unit 19 that identifies the peak μ slip rate; a variation calculation unit 20 that determines the variation of the peak μ slip rate for each part; and an optimal parameter identification unit 21 that identifies the parameters that minimize the variation determined by the variation calculation unit 20.

Each of these components is realized by having the processor of a computer equipped with a processor, a hard disk, memory, an input device (e.g., a keyboard or mouse), a display device (e.g., a display), etc. execute a program stored on the hard disk, etc.

The tire evaluation method of this embodiment will be explained based on the flowchart in Figure 2.

First, in ST1, the tire model acquisition unit 11 acquires a three-dimensional tire model 30 as shown in FIG. 3. The tire model 30 is a finite element model that is the subject of analysis by the finite element method, and is divided into a mesh of multiple elements with nodes at the vertices of these elements. The finite element model acquired by the tire model acquisition unit 11 is created using a known method for creating finite element models based on CAD drawings, etc.

Each element and each node is assigned an element number, node number, node coordinates, and physical property values (e.g., density, Young's modulus, Poisson's ratio, stiffness, etc.). Here, stiffness is a parameter that affects the peak μ slip ratio, which will be described later. The tread portion will be divided into multiple parts as will be described later, and a different stiffness is set for each part. However, the same stiffness may be set for multiple parts. The stiffness may also be set after the tread portion is divided.

Physical quantities that represent rigidity include hardness (e.g., durometer hardness as defined in JIS K 6253), elastic modulus (e.g., elastic modulus as defined in JIS K 6254), modulus (100% modulus or 300% modulus) (e.g., modulus as defined in JIS K 6251), etc. In this embodiment, rigidity refers to any of these.

As shown in FIG. 3, the tire model 30 has a tread portion 31. In the tread portion 31, a plurality of main grooves extending in the tire circumferential direction are formed, and a plurality of ribs are formed spaced apart from the main grooves. Each rib extends in the tire circumferential direction. Furthermore, in the tread portion 31, a plurality of lateral grooves extending in the tire width direction are provided, which are periodically arranged in the tire circumferential direction. A tread pattern is formed in the tread portion 31 by these grooves.

In a tread pattern, multiple grooves with specific shapes are arranged in the circumferential direction of the tire. These specific shapes are called one pitch, and the length of one pitch in the circumferential direction of the tire is called the pitch length. The pitch length is indicated by L in Figure 3.

The tire model acquisition unit 11 acquires multiple tire models. In this embodiment, the multiple tire models acquired by the tire model acquisition unit 11 have different stiffnesses in each part of the tread.

Next, in ST2, the road surface model acquisition unit 12 acquires a road surface model against which the tire model is pressed in the behavior analysis. The road surface model is also a finite element model. Special road surface conditions (e.g., uneven conditions or wet conditions) are set in the road surface model as necessary.

Next, in ST3, the part setting unit 13 divides the tread portion of the tire model into multiple parts. Here, the definition of "part" is arbitrary. For example, one rib may be defined as one part, or one block may be defined as one part. Also, one rib or block may be divided into even smaller parts, and each part may be defined as a part. Also, parts may be defined by the distance from the tire contact edge.

Next, in ST4, the boundary condition setting unit 14 sets various boundary conditions for analyzing tire behavior. The boundary conditions include the tire internal pressure, the load on the tire, the friction coefficient between the tire and the road surface, the rim assembly conditions, the slip angle, the running speed, etc. The boundary conditions used may be conditions input from an input device or conditions stored on a hard disk.

Note that the actual friction coefficient changes depending on the pressure between the tire and the road surface and on the sliding speed of the tire. Therefore, it is desirable to set the friction coefficient as one that depends on the pressure and sliding speed. For example, the relationship between the friction coefficient, pressure, and sliding speed is obtained in advance by experiment or the like, and a table of friction coefficients is created and set with pressure as rows and sliding speed as columns. For friction coefficients of pressures and sliding speeds that are not in the table, the friction coefficient of the closest pressure and sliding speed may be substituted, or an approximate formula for the friction coefficient, pressure, and sliding speed values in the table may be found and the coefficient may be calculated from the approximate formula. However, the friction coefficient may also be a constant value that does not depend on pressure or sliding speed.

Next, in ST5, the behavior analysis unit 15 performs behavior analysis using the finite element method. For example, the application of longitudinal and lateral forces to a tire pressed against a road surface is reproduced, and the behavior of the tire at that time is analyzed. In the analysis, physical quantities such as ground pressure and slip speed at each node are determined over time. Specific methods of behavior analysis include dynamic rolling analysis using an explicit method, and quasi-static analysis and steady-state transport analysis (mixed Lagrangian/Euler method) using an implicit method. In a detailed analysis focusing on the behavior of the contact patch as in this embodiment, it is desirable to use an implicit method, which has excellent solution stability.

As a result of this behavior analysis, the node number and the physical quantity of each node are output. There are various physical quantities, such as shear stress, contact pressure, sliding velocity, and area assigned to the node.

Next, in ST6, the classification unit 16 classifies each node of the contact surface into either an adhesive region or a slippery region. Here, an adhesive region is a region of the tire's contact surface where it is determined that the tire is not slipping on the road surface. A slippery region is a region where it is determined that the tire is slipping on the road surface.

The classification of each node on the contact patch into an adhesive or slippery zone is based on the sliding speed of the node (the speed of the node relative to the road surface) determined by behavior analysis. Specifically, the allowable sliding speed γ defined by the following formula 1 is used as the classification criterion. If the sliding speed of a node is slower than this allowable sliding speed γ, the node is classified into the adhesive zone. On the other hand, if the sliding speed of a node is faster than the allowable sliding speed γ, the node is classified into the slippery zone. If the sliding speed of a node matches the allowable sliding speed γ, it is up to the user to decide whether to classify the node into a slippery zone or an adhesive zone.

Here, f is an arbitrarily determined slip tolerance value, ω is the angular velocity of the tire rotation, and R is the effective radius of the tire (the distance from the tire's center of rotation to the road surface). Note that ω x R is equal to the tire's rolling speed (the distance the tire travels per unit time due to its own rotation, assuming that the tire does not slip on the road surface). When the tire is braked, the tire's rolling speed changes over time, so the allowable slip speed γ also changes over time.

As a specific example, consider a case where the slip tolerance value f is 0.02 and the tire rolling speed is 40 km/hour. In this case, the allowable slip speed γ is 444 mm/second. Therefore, if the slip speed of a node is slower than 444 mm/second, the node is classified as being in the adhesive region. On the other hand, if the slip speed of a node is faster than 444 mm/second, the node is classified as being in the slip region.

When each node is classified as an adhesive or slippery area in this manner, the tire's contact surface is divided into adhesive areas 32 and slippery areas 33, as shown in Figure 4.

Next, in ST7, the nodes are classified by part and area in the integrating unit 17, and the physical quantities of each node within the classified range are integrated. In other words, the physical quantities of multiple nodes classified into the same part and the same area are integrated for each area of each part. The physical quantities are the physical quantities obtained as a result of the behavior analysis.

As an example of the display of the integration results by the integration unit 17, FIG. 5 shows the relationship between the slip ratio and the braking force of a tire model having four ribs, where one rib of the tread is considered as one part.

In this case, the part setting unit 13 classifies each node on the contact surface of the tire model as belonging to one of four ribs (parts). The classification unit 16 also classifies each node as being included in one of the regions (adhesive region or slipping region) at each slip ratio. The integration unit 17 then integrates the magnitude of the braking force of the multiple nodes classified into each group and region at each slip ratio. When the results are displayed, they will look like Figure 5, with the slip ratio on the horizontal axis and the braking force on the vertical axis.

Curve p in Figure 5 shows the change in braking force across the entire tire. Curve q shows the change in braking force generated in the tire's adhesive region. Therefore, the height of curve q indicates the magnitude of braking force generated in the tire's adhesive region at that slip ratio, and the height of the portion sandwiched between curves q and p indicates the magnitude of braking force generated in the tire's slipping region at that slip ratio. Additionally, the height of each region shown as rib 1 to rib 4 in Figure 5 indicates the magnitude of braking force generated in each rib at that slip ratio. In this way, it is possible to know the magnitude of braking force generated in each region of each rib (part), and how this changes with changes in slip ratio.

The slip ratio is the ratio of the difference between the tire's forward speed and rolling speed to the tire's forward speed; the smaller this ratio is, the closer the tire's forward speed and rolling speed are. When the tire is slipping and not rotating, the slip ratio is 100%, and when the tire's forward speed and rolling speed are the same, the slip ratio is 0%. Braking force is the shear stress in the fore-and-aft direction when the brakes are applied to a rolling tire.

Next, in ST8, the μ-S diagram creation unit 18 creates a μ-S diagram for each part (each rib in the case of FIG. 6) as shown in FIG. 6. The μ-S diagram shows the relationship between the slip rate S and the friction coefficient μ. The friction coefficient μ is calculated by dividing the braking force (the braking force in the adhesion area plus the braking force in the slip area) by the load.

As can be seen from Figure 6, a peak appears on the μ-S diagram where the friction coefficient μ is at its maximum. The friction coefficient μ at this peak is referred to as "peak μ", and the slip ratio S when the friction coefficient reaches its peak μ is referred to as the "peak μ slip ratio". In Figure 6, the slip ratio indicated by the dashed line drawn down the horizontal axis from the peak is the peak μ slip ratio. As can be seen from Figure 6, the peak μ slip ratio generally differs from part to part.

The μ-S diagram changes depending on the rigidity of the rubber. As the rigidity of the rubber (e.g. hardness, elasticity or modulus) decreases, the μ-S diagram deforms toward the side with a larger slip ratio (i.e., toward the right in Figure 6), and the peak μ slip ratio increases.

Next, in ST9, the peak μ slip rate for each part is identified by the μ-S diagram analysis unit 19. A single tire has multiple parts, and the peak μ slip rate is identified for all parts.

Next, in ST10, the variation of the peak μ slip ratio for each part is calculated by the variation calculation unit 20. In this embodiment, the variation is calculated as the ratio of the difference (absolute value) between the average value of the peak μ slip ratio and the maximum or minimum value of the peak μ slip ratio to the average value. In other words, the variation d is calculated by the following formula.

Here, a is the average value of the peak μ slip ratio, and m is the maximum or minimum value of the peak μ slip ratio, whichever is greater in difference from the average value. However, variance, standard deviation, etc. may also be calculated as the variation.

Next, in ST11, it is determined whether the calculation of the peak μ slip rate variation for all tire models has been completed. If not (No in ST11), steps ST3 to ST10 are executed for the next tire model. Then, if the calculation of the peak μ slip rate variation for all tire models has been completed (Yes in ST11), the process proceeds to the next step, ST12.

In ST12, the optimal parameter identification unit 21 identifies a tire model that minimizes the variation found by the variation calculation unit 20. By identifying the tire model that minimizes the variation, parameters that minimize the variation are identified in ST13. These parameters are referred to as "optimum parameters." In this embodiment, the stiffness of each part of the tread portion is identified as the optimal parameter.

The parameters (rigidity) obtained by the above method are used in tire design. Specifically, the rubber compounding for each part of the tread is determined so that the rigidity of each part matches the optimal parameters. This ensures that the peak μ slip rate of each part is consistent throughout the tire. Note that tire design may be performed by the program following ST13, or may be performed manually by the designer.

By having the peak μ slip rate of each part be consistent across the entire tire, the friction coefficient of each part will be at its peak μ when the same slip rate is applied. Therefore, if the slip rate reaches its peak μ slip rate when braking force is applied to the tire, the friction coefficient will be at its peak μ in all parts that are in contact with the ground at that time, and maximum braking force will be generated across the entire contact surface. By having the peak μ slip rate of each part be consistent across the entire tire, this effect will be achieved regardless of which part is in contact with the ground when braking force is applied to the tire.

In a tire designed in this manner, the variation d of the peak μ slip ratio calculated by the above formula 2 is preferably within 2%, and more preferably within 1%.

As described above, the tire evaluation method of this embodiment includes a step of acquiring multiple tire models with different parameters. The tire evaluation method further includes a step of dividing the tread portion of the multiple tire models into multiple parts, a step of obtaining a μ-S diagram for each part based on the results of the behavior analysis of the tire model and obtaining the peak μ slip rate of each part, and a step of obtaining the variation in the peak μ slip rate of each part. This allows the designer to know the variation in the peak μ slip rate for multiple tire models with different parameters. A tire with a smaller variation in the peak μ slip rate generates a larger braking force at all parts that come into contact with the ground, so the designer can know which tire model has better braking performance and use this information in tire design.

In addition, in this embodiment, the tire evaluation method includes a step of identifying a tire model that minimizes the variation in peak μ slip rate. Therefore, the designer can easily know which of multiple tire models has good braking performance.

In addition, in this embodiment, the parameters of the tire model that minimize the variation in the peak μ slip rate are identified, so that the designer can use those parameters to design a tire with good braking performance.

Here, since the stiffness of the tread portion affects the peak μ slip rate, multiple tire models with different stiffnesses in each part of the tread portion are obtained in ST1, and the stiffness of each part of the tread portion is identified as the optimal parameter in ST13, making it possible to effectively design a tire with good braking performance.

Various modifications can be made to the above embodiments.

For example, the pitch length of the tread pattern affects the rigidity of each part of the tread, and thus the peak μ slip rate. The shorter the pitch length, the lower the rigidity of each part and the higher the peak μ slip rate.

As a modification, the tire model acquisition unit 11 may acquire multiple tire models with different pitch lengths. Note that the multiple tire models with different pitch lengths may be created one by one, or may be generated by morphing from a reference tire model.

In this modified example, in ST1 of FIG. 2, multiple tire models with different pitch lengths are obtained. Next, the same steps ST1 to ST11 as in the above embodiment are executed. Then, in ST12, the optimal parameter identification unit 21 identifies the tire model that minimizes the variation in peak μ slip rate, and in ST13, the parameters of that tire model are identified as optimal parameters. In this modified example, the pitch length is identified as the optimal parameter.

The tire is designed based on the pitch length thus determined as the optimal parameter. This allows the design of a tire with consistent peak μ slip rates for each part.

Reference Signs List 10: tire evaluation device, 11: tire model acquisition unit, 12: road surface model acquisition unit, 13: part setting unit, 14: boundary condition setting unit, 15: behavior analysis unit, 16: classification unit, 17: integration unit, 18: μ-S diagram creation unit, 19: μ-S diagram analysis unit, 20: variation calculation unit, 21: optimal parameter identification unit, 30: tire model, 31: tread portion, 32: adhesion region, 33: slippage region

Claims (4)

obtaining a plurality of tire models having different parameters;
For each of the plurality of tire models,
Dividing a tread portion of the tire model into a plurality of portions;
a step of contacting the tire model with a road surface model and analyzing the behavior of the tire model by a finite element method;
determining a relationship between the slip ratio and the friction coefficient for each of the portions based on the results of the behavior analysis, and determining a peak μ slip ratio, which is the slip ratio when the friction coefficient is maximum in each portion;
determining a variation in the peak μ slip ratio for each portion;
identifying a tire model that minimizes the variation in peak μ slip ratio from among the plurality of tire models;
A tire evaluation method including: The tire evaluation method according to claim 1 , further comprising the step of identifying parameters of a tire model that minimize the variation in the peak μ slip rate. 3. The tire evaluation method according to claim 2 , further comprising a step of specifying stiffness of each portion of the tread portion as a parameter of a tire model that minimizes the variation in the peak μ slip rate. The tread portion has a tread pattern in which a plurality of grooves are periodically arranged in the tire circumferential direction,
The tread pattern has a pitch length, which is a length of one pitch in a tire circumferential direction,
The tire evaluation method according to claim 2 , further comprising the step of identifying the pitch length as a parameter of a tire model that minimizes the variation in the peak μ slip rate.

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