JP6871572B2 - Tire braking simulation method - Google Patents

Description

The present invention relates to a tire braking simulation method, and more particularly to a method for calculating a tire braking state when a braking force is applied to a tire traveling on a road surface by ABS using a computer.

The following Non-Patent Document 1 proposes a simulation method for reproducing the control of ABS that gives a braking force to a tire by using a computer. In this kind of simulation method, first, the calculation model of the tire and ABS is input to the computer. Next, the computer calculates the running state of the tire. Then, the computer applies the braking force of ABS, which changes based on a predetermined condition, to the tire in the running state, and calculates the physical quantity of the tire.

Kunio Kobayashi, 6 outsiders, "Research on Modeling of Friction Force between Tires and Road Surface and ABS Control", [online], Department of Mechanical Engineering, Faculty of Engineering, Tokyo City University, Mechanical Dynamics Laboratory, [Searched on February 2, 2017] , Internet <URL: http: //www.mdl.me.tcu.ac.jp/research/20_B_2.pdf>

In the general algorithm of ABS (system), the braking force is decreased when the tire slip ratio is increased, while the braking force is increased when the tire slip ratio is decreased. On the other hand, it takes a certain amount of time from the change of the braking force in ABS to the next change of the braking force. In the conventional simulation method, such an actual situation is not taken into consideration, and there is room for further improvement in order to accurately calculate the braking condition of the tire.

The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a simulation method capable of accurately calculating the braking state of a tire when a braking force is applied by ABS.

The present invention is a method for calculating the braking state of a tire when a braking force is applied to a tire traveling on a road surface by ABS, and the computer is provided with the braking force of the ABS and the braking force of the ABS. The computer includes a step of defining a calculation model for calculating the physical quantity of the tire subjected to the braking force, and the computer uses the calculation model to calculate the physical quantity of the tire in a step of a first minute time Δt1. A step of calculating while developing the time, and a step of changing the braking force of the ABS of the calculation model in a step of a second minute time Δt2 larger than the first minute time Δt1 based on the physical quantity of the tire. And execute.

In the tire braking simulation method according to the present invention, the step of calculating the physical quantity includes the step of calculating the slip ratio of the tire, and the step of changing the braking force of the ABS is such that the slip ratio of the tire is determined. The step of reducing the braking force of the ABS when it is larger than a predetermined target slip ratio, and increasing the braking force of the ABS when the slip ratio of the tire is smaller than the target slip ratio. It may include a step of performing.

In the tire braking simulation method according to the present invention, a μ-S curve showing the relationship between the friction coefficient μ of the tire and the slip ratio S is shown to the computer prior to the step of changing the braking force of the ABS. Between the step of inputting and the first slip ratio at which the friction coefficient μ of the μ-S curve is maximized and the second slip ratio at which the friction coefficient μ of the μ-S curve is minimized. It may further include a step of defining the target slip coefficient.

In the tire braking simulation method according to the present invention, the ABS includes a disc portion that rotates with the tire and a pad portion that contacts the disc portion, and the step of calculating the physical quantity includes the disc portion and the disc portion. A step of calculating the braking force by multiplying the coefficient of friction with the pad portion and the pressing force of the pad portion on the disc portion may be further included.

In the tire braking simulation method according to the present invention, a temperature dependence may be defined in which the friction coefficient between the disc portion and the pad portion increases as the temperature of the disc portion rises.

The tire braking simulation method of the present invention includes a step of defining a calculation model for calculating the braking force of ABS and the physical quantity of the tire subjected to the braking force in a computer. The computer uses a calculation model to calculate the physical quantity of the tire while developing it over time in the step of the first minute time Δt1, and based on the physical quantity of the tire, the braking force of the ABS of the calculation model is first minute. The step of changing in the step of the second minute time Δt2 larger than the time Δt1 is executed.

In the tire braking simulation method of the present invention, the physical quantity of the tire subjected to the ABS braking force is taken into consideration in consideration of the time interval (time lag) from the change of the braking force by the ABS to the next change of the braking force. Can be calculated. Therefore, the tire braking simulation method of the present invention can accurately calculate the tire braking state when a braking force is applied by ABS.

It is a block diagram which shows an example of the computer which carries out the tire braking simulation method. It is a flowchart which shows an example of the processing procedure of the tire braking simulation method. It is a conceptual diagram which shows an example of a tire. It is a conceptual diagram which shows an example of ABS. It is a flowchart which shows an example of the processing procedure of the μ-S curve definition process. It is a graph which shows an example of a μ-S curve. It is a flowchart which shows an example of the processing procedure of a physical quantity calculation process. It is a flowchart which shows an example of the processing procedure of the brake oil pressure calculation process. It is a flowchart which shows an example of the processing procedure of the braking force changing process. It is a graph which shows the relationship between the average slip ratio of the simulation of an Example and a comparative example, and the average slip ratio of an experimental example. It is a graph which shows the relationship between the standard deviation of the slip ratio of the simulation of an Example and a comparative example, and the standard deviation of the slip ratio of an experimental example. It is a graph which shows the relationship between the braking distance of the simulation of an Example and a comparative example, and the braking distance of an experimental example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The tire braking simulation method of the present embodiment (hereinafter, may be simply referred to as a "simulation method") is a tire braking when a braking force is applied to a tire traveling on a road surface by ABS (anti-lock braking system). This is a method for calculating the situation using the computer 1.

FIG. 1 is a block diagram showing an example of a computer 1 in which the simulation method of the present embodiment is implemented. The computer 1 of the present embodiment includes an input unit 2 as an input device, an output unit 3 as an output device, and an arithmetic processing device 4 for calculating the physical amount of the tire, etc., and calculates the braking status of the tire. It is configured as a braking simulation device 1A.

For the input unit 2, for example, a keyboard, a mouse, or the like is used. For the output unit 3, for example, a display device, a printer, or the like is used. The arithmetic processing device 4 includes an arithmetic unit (CPU) 4A that performs various arithmetic operations, a storage unit 4B that stores data, programs, and the like, and a working memory 4C.

The storage unit 4B is a non-volatile information storage device including, for example, a magnetic disk, an optical disk, an SSD, or the like. The storage unit 4B is provided with a data unit 5 and a program unit 6.

The data unit 5 includes an initial data unit 5A for storing information about the tire to be evaluated and ABS, a tire model input unit 5B for inputting a tire model, an ABS model input unit 5C for inputting an ABS model, and a μ-S curve. The μ-S curve input unit 5D to which is input, the physical quantity input unit 5E to which the physical quantity calculated by the calculation unit 4A is input, and the braking force switch input unit 5F to which the braking force switch is input are included.

The program unit 6 is a program executed by the arithmetic unit 4A. The program unit 6 includes a tire model setting unit 6A for setting a tire model, an ABS model setting unit 6B for setting an ABS model, a μ-S curve setting unit 6C for setting a μ-S curve, and a tire braking status. It is configured to include a physical quantity calculation unit 6D for calculating the above.

FIG. 2 is a flowchart showing an example of the processing procedure of the simulation method. In the simulation method of the present embodiment, the physical quantity of the tire and the like are calculated by the computer 1 while time-evolving in a predetermined step of the first minute time Δt1. The first minute time Δt1 can be appropriately set according to the required simulation accuracy. The first minute time Δt1 of this embodiment is set to, for example, 0.00001 to 0.001 seconds (0.0001 seconds in this embodiment).

In the simulation method of the present embodiment, first, a calculation model for calculating the braking force of ABS and the physical quantity of the tire subjected to the braking force is defined in the computer 1 (step S1). The calculation model includes a tire model that models a tire and an ABS model that models ABS.

In step S1, first, as shown in FIG. 1, information about the tire 11 and ABS stored in the initial data unit 5A is input to the working memory 4C. Further, the tire model setting unit 6A and the ABS model setting unit 6B are read into the working memory 4C. Then, the tire model setting unit 6A and the ABS model setting unit 6B are executed by the calculation unit 4A.

As the tire model of this embodiment, a model of a single-wheel tire is exemplified. The tire model is not limited to such an aspect. The tire model is defined by the following equations (1) to (4). FIG. 3 is a conceptual diagram showing an example of the tire 11.

ここで、
Ｓ：タイヤのスリップ率
Ｍ：タイヤが装着される車両の質量（kg）
ｇ：重力定数（ｍ/ｓ²）
μ：タイヤの摩擦係数
Ｉ：タイヤの慣性モーメント（kg・ｍ²）
Ｒ：タイヤ半径（ｍ）
Ｖ_vehicle：車体速度（ｍ／ｓ）
Ｖ_wheel：タイヤ速度（ｍ／ｓ）
Ａ：定数
Ｔｒ：計算パラメータ

here,
S: Tire slip ratio M: Weight of the vehicle on which the tire is mounted (kg)
g: Gravitational constant (m / s ² )
μ: Tire friction coefficient I: Tire moment of inertia (kg ・ m ² )
R: Tire radius (m)
V _vehicle : Body speed (m / s)
V _wheel : Tire speed (m / s)
A: Constant Tr: Calculation parameter

The above equation (1) defines the tire slip ratio S. The slip ratio S is _{obtained by subtracting the tire speed V wheel} (specified by the above formula (3) _{) from the vehicle} body speed V vehicle (specified by the above formula (2)) and dividing by the _{vehicle body speed V vehicle.} It is required by doing.

The above equation (2) defines the balance of forces in the traveling direction of the tire for each step of the first minute time Δt1. In the above equation (2), the left side obtained by multiplying the mass M of the vehicle and the acceleration of the _vehicle body (that is, the derivative of the vehicle body speed V vehicle) indicates the force in the traveling direction of the tire model. In the above equation (2), the right side obtained by multiplying -1, the mass M of the vehicle, the gravitational constant g, and the friction coefficient μ (S) of the tire indicates the force in the direction opposite to the traveling direction. The tire friction coefficient μ (S) is a function of the slip ratio S and is defined by the following equation (11).

The above equation (3) defines the balance of torque in the rotation direction of the tire for each step of the first minute time Δt1.

In the above equation (3), the left side obtained by multiplying the moment of inertia I of the tire by the ratio of the tire acceleration (that is, the _{differential of the tire speed V wheel} ) and the tire radius R is the time of the angular momentum in the rotation direction of the tire. It shows a change. In the above equation (3), the brake torque τ (defined by the following equation (7)) is subtracted from the product of the vehicle mass M, the gravitational constant g, the tire radius R, and the tire friction coefficient μ (S). The right side shows the torque in the rotational direction of the tire. The tire friction coefficient μ (S) is a function of the slip ratio S and is defined by the following equation (11). In the above equation (3), both sides are multiplied by R / I, MgR ² / I is replaced with A based on the above equation (4), and τ / MgR is further based on the above equation (5). By replacing it with Tr, it can be simplified as in the above equation (6).

In the above equation (4), the constant A is a parameter set for easy simulation calculation, and is the mass M of the vehicle, the gravitational constant g, the square R ^{2 of the} tire radius, and the moment of inertia I of the tire. Calculated from. Such a constant A can be calculated from the measured value. In the above equation (5), the calculation parameter Tr is also a parameter set for the same purpose as the constant A, and is calculated from the brake torque τ, the mass M of the vehicle, the gravitational constant g, and the radius R of the tire. Such a calculation parameter Tr can be obtained by multiplying the brake torque τ by a coefficient that can be calculated from the measured value. Therefore, by calculating in advance before the simulation calculation is performed, for example, in a processing routine using a simplified formula of the above formula (3), the constant A can be used instead of the above formula (6). And the coefficient do not need to be calculated repeatedly, so the calculation time can be shortened.

From the above equations (1) to (3), it is possible to define a tire model capable of calculating the tire 11 that rolls on the road surface and brakes. The tire model is stored in the tire model input unit 5B (shown in FIG. 1).

FIG. 4 is a conceptual diagram showing an example of ABS. The ABS 12 includes a disc portion 13 that rotates with the tire 11 (shown in FIG. 3) and a pad portion 14 that contacts the disc portion 13. The greater the pressing force of the pad portion 14 on the disc portion 13, the greater the braking force (brake torque τ) of the tire 11. The pressing force of the pad portion 14 is adjusted by the magnitude of the brake oil pressure P of the hydraulic unit 15 connected to the pad portion 14. The magnitude of the brake oil pressure P of the hydraulic unit 15 is controlled by a control means (not shown).

In the general algorithm of ABS (system) 12, when the slip ratio S of the tire 11 (shown in FIG. 3) becomes large, the pressing force (brake oil pressure P) of the pad portion 14 is reduced to reduce the braking force (brake torque τ). ) Is decreasing. On the other hand, when the slip ratio S of the tire 11 becomes smaller, the pressing force (brake oil pressure P) of the pad portion 14 is increased to increase the braking force. As a result, the ABS 12 can bring the tire slip ratio S during braking close to the ideal slip ratio (target slip ratio S ₀ described later), so that the occurrence of slippage due to the locking of the tire 11 can be reduced. The ABS model of this embodiment is defined by the following equations (7) to (10).

ここで、
Ｓ：タイヤのスリップ率
Ｓ₀：タイヤの目標スリップ率
μ：タイヤの摩擦係数
Ｖ_wheel：タイヤ速度（ｍ／ｓ）
τ：ブレーキトルク（Ｎ）
Ｐ：ブレーキ油圧（ＭＰａ）
Ｔ：ディスク部の温度（℃）
μ_pad（Ｔ）：ディスク部とパッド部との間の摩擦係数
μ₀：パッド部の基準摩擦係数
Ｔ_atm：外気温（℃）
Ｔ₀：ディスク部の基準温度（℃）
Ｂ、Ｃ、Ｄ、Ｅ、α：定数

here,
S: Tire slip rate S ₀ : Tire target slip rate μ: Tire friction coefficient V _wheel : Tire speed (m / s)
τ: Brake torque (N)
P: Brake oil pressure (MPa)
T: Disk temperature (° C)
μ _pad (T): Friction coefficient between the disc part and the pad part μ ₀ : Reference friction coefficient of the pad part T _atm : Outside air temperature (° C)
T ₀ : Reference temperature (° C) of the disc
B, C, D, E, α: constant

The above equation (7) defines the brake torque τ. _{The brake torque τ is such that the brake oil pressure P is multiplied by the friction coefficient μ pad} (T) (specified by the above equation (8)) between the disc portion and the pad portion when the temperature of the disc portion is T. Defined by.

_{The above equation (8) defines a friction coefficient μ pad} (T) between the disc portion 13 and the pad portion 14, which changes depending on the temperature T of the disc portion 13. Α (T−T ₀ ) in the above equation (8) indicates an increase in the friction coefficient of the pad portion 14 defined by multiplying the rising temperature (T−T _{0) of the disc portion 13 by the constant α.} .. _{By adding the reference friction coefficient μ 0} of the pad portion 14 to the increase in the friction coefficient (α (T−T ₀ )), the disc portion 13 and the pad portion 14 at the temperature T of the disc portion 13 The coefficient of friction μ _pad (T) between them is obtained. Therefore, the friction coefficient μ _pad (T) is defined as a temperature dependence that increases as the temperature T of the disk portion rises.

The above equation (9) defines the rate of change of the temperature T of the disk unit 13. In the above formula (9), _{D · μ multiplied by the constant D, the μ pad} (T) of the above formula (8), the brake oil pressure P, and the tire speed V _wheel (specified by the above formula (3)). _{The pad} (T), P, and V _wheels show frictional heat generation of the disc portion 13 due to contact with the pad portion 14. In this frictional heat generation (constant D · μ _pad (T) · P · V _wheel ), the constant D is a parameter indicating the ease of heat generation. In the above equation (9), E. (T-T _atm ), which is obtained by multiplying the constant E by the temperature T of the disc portion 13 _{minus the} outside air temperature T atm, indicates the heat dissipation of the disc portion 13. In this heat dissipation (E · (T—T _atm )), the constant E is a parameter indicating the ease of heat dissipation. By subtracting heat dissipation (E. (T-T _atm )) from frictional heat generation (D, μ _pad (T), P, V _wheel ), the above equation (9) changes for each step of the first minute time Δt1. The rate of change of the temperature T of the disk to be used is defined.

The above equation (10) defines the rate of change of the brake oil pressure P. In the above equation (10), when the slip ratio S of the tire 11 _{is smaller than the target slip ratio S 0 of the} tire (that is, S <S ₀ ), in the brake oil pressure calculation step S6 described later, the step of the first minute time Δt1. For each, a brake oil pressure P that increases at a rate of a positive constant B is defined. On the other hand, when the slip ratio S of the tire 11 _{is larger than the target slip ratio S 0 of the} tire (that is, S> S ₀ ), the brake decreases at a rate of a negative constant −C for each step of the first minute time Δt1. The oil pressure P is defined.

From the above equations (7) to (10), it is possible to define an ABS model in which the braking force (brake torque τ) of ABS can be changed according to the slip ratio S. Then, by substituting the brake torque τ of the above equation (7) into the above equation (3) of the tire model, it is possible to calculate the tire model that stops by the braking force of the ABS. The ABS model is stored in the ABS input unit 2C (shown in FIG. 1).

In the above formula (4), the above formula (9), and the above formula (10), the constants A to E and the constant α are, for example, actually measured values of a vehicle equipped with ABS 12 and equipped with tires 11. Alternatively, the estimated value is used as the initial value, and the calculation result (average value of the slip ratio S) using the above-mentioned tire model and ABS model is identified so as to approximate the actually measured average value of the slip ratio S. As an example of the identification method, as described above, as described above ^{, the measurement results of the vehicle mass M, the gravitational constant g, the square R 2 of the} tire radius, and the moment of inertia I of the tire are substituted into the above equation (4). It is determined by. Further, as an example of the identification method of the constants B and C, first, the time change of the brake oil pressure during braking is measured, and a graph showing the relationship between the brake oil pressure P and the time t is obtained. Next, in the obtained graph, at least one section in which the brake oil pressure P is increasing is extracted, and the positive average value B ₀ of the slope (brake pressure P / time t) of the graph obtained for each of these sections is obtained. calculate. Similarly, in the obtained graph, at least one section in which the brake oil pressure is decreasing is extracted, and the negative average value C ₀ of the slope of the graph obtained for each of these sections is calculated. Then, a simulation is performed to calculate the average value of the slip ratio S while changing the constants B and C in the following range, and the calculation result of the average value of the slip ratio S and the actually measured average value of the slip ratio S are obtained. The constants B and C with the closest optimum values are specified.
Range of constant B: 0.9B ₀ ≤ B ≤ 1.1B _{0 (incremental value of} B: 0.01B ₀ )
Range of the constant _{C: 0.9C 0 ≦ B ≦ 1.1C} 0 (C increment: 0.01 C ₀₎

By identifying the constants A to E and the constant α, a tire model that models the tire to be evaluated and an ABS model that models the ABS to be evaluated are specified. As described above, in the calculation model (tire model and ABS model) of the present embodiment, by appropriately setting the constants A to E and the constant α, for example, tires and ABS having different performances for each manufacturer can be obtained. Since it can be set individually, it has excellent versatility. The above formulas (1) to (10) are not limited to the above-described aspects, and may be appropriately modified as necessary.

Next, in the simulation method of the present embodiment, an μ-S curve showing the relationship between the tire friction coefficient μ and the slip ratio S is input to the computer 1 (μ-S curve definition step S2). FIG. 5 is a flowchart showing an example of the processing procedure of the μ-S curve definition step S2.

In the μ-S curve definition step S2 of the present embodiment, first, the friction coefficient μ and the slip ratio S of the tire are measured (step S21). As an example of the method of measuring the friction coefficient μ and the slip ratio S of the tire, a drum tester is used to make the rotation speed of the drum different from the rotation speed of the tire, so that the friction coefficient μ is different for each different slip ratio S. Is measured. The friction coefficient μ and the slip ratio S of the tire are stored in the physical quantity input unit 5E.

Next, in the μ-S curve definition step S2 of the present embodiment, the μ-S curve is obtained (step S22). In step S22, as shown in FIG. 1, the friction coefficient μ and the slip ratio S of the tire stored in the physical quantity input unit 5E are read into the working memory 4C. Further, the μ-S curve setting unit 6C is read into the working memory 4C. Then, the μ-S curve setting unit 6C is executed by the calculation unit 4A.

In step S22, the μ-S curve is obtained by plotting the friction coefficient μ of the tire for each slip ratio S. FIG. 6 is a graph showing an example of a μ-S curve. The μ-S curve is stored in the μ-S curve input unit 5D.

Next, in the μ-S curve definition step S2 of the present embodiment, the computer 1 defines a function of the μ-S curve representing the μ-S curve (step S23). In step S23, as shown in FIG. 1, the −S curve stored in the μ—S curve input unit 5D is read into the working memory 4C. Further, the μ-S curve setting unit 6C is read into the working memory 4C. Then, the μ-S curve setting unit 6C is executed by the calculation unit 4A. The function of the μ-S curve is defined by the following equation (11).

ここで、
μ：タイヤの摩擦係数
Ｓ：タイヤのスリップ率
Ｓ_max：摩擦係数μが最大となる第１スリップ率
Ｅ_a、Ｅ_b、Ｅ_c：定数

here,
μ: Tire friction coefficient S: Tire slip rate S _max : First slip rate that maximizes the friction coefficient μ E _a , E _b , E _c : Constant

The function of the μ-S curve is a first function that approximates the μ-S curve between the first slip ratio S _max that maximizes the friction coefficient μ and the second slip ratio S _{min that minimizes the friction coefficient μ.} (Upper side of the above equation (11)) and a second function (lower side of the above equation (11)) that approximates a μ-S curve larger than _{the first slip coefficient S max.}

The constant E _a , for example, causes the first function (upper side of the above equation (11)) to be fitted to the μ-S curve between _{the first slip ratio S max} and the second slip ratio S _{min by the least squares method.} Can be identified by The constants E _b and E _c can be identified by linearly approximating the second function (lower side of the above equation (11)) to a _{μ-S curve larger than the first slip ratio S max} by the method of least squares. .. The constants E _b and E _c are every slip ratio S (for example, 0.2, 0.4, 0.6 and 0.8) at regular intervals for a slip ratio S larger than the first slip ratio S _max. It may be identified based on the straight line connecting the friction coefficient μ specified in.

By such a function of the μ-S curve, the computer 1 can uniquely identify the friction coefficient μ and the slip ratio S of the tire. The μ-S curve function is input to the μ-S curve input unit 5D.

Next, in the simulation method of the present embodiment, the initial values of the calculation models (tire model and ABS model) are input to the computer 1 prior to calculating the physical quantity of the tire (step S3). In step S3 of the present embodiment, initial values necessary for calculating the tire 11 that rolls and brakes the road surface are input to the constants and variables of the above equations (1) to (10).

The constants and variables to which the initial values are input include, for example, the mass M of the vehicle on which the tire is mounted, the gravity constant g, the friction coefficient μ of the tire, the inertial moment I of the tire, the tire radius R, the vehicle body speed V _vehicle , and the tire. The speed V _wheel , the temperature T of the disc portion, the reference friction coefficient μ ₀ of the pad portion, the outside temperature _Tire , and the reference temperature T ₀ of the disc portion. Further, each initial value can be appropriately set according to the braking condition of the tire to be calculated by the simulation method of the present embodiment. The initial value of each constant is stored in the initial data unit 5A (shown in FIG. 1).

Next, in the simulation method of the present embodiment, the initial value of the braking force switch is input to the computer 1 (step S4). The braking force switch is for controlling whether or not to increase the braking force of the ABS (in the present embodiment, the brake torque τ of the above equation (7)). As the value of the braking force switch, "initial value (for example, 0)", "large (for example, 1)", or "small (for example, 2)" is input. In the simulation method of the present embodiment, the brake oil pressure P for calculating the braking force of ABS (brake torque τ of the above equation (7)) is set based on the value of the braking force switch. The braking force switch is stored in the braking force switch input unit 5F.

Next, in the simulation method of the present embodiment, the computer 1 calculates the physical quantity of the tire using the calculation model (physical quantity calculation step S5). In the physical quantity calculation step S5, as shown in FIG. 1, the tire model stored in the tire model input unit 5B, the ABS model stored in the ABS model input unit 5C, and the initial data unit 5A are stored. The initial value is read into the working memory 4C. Further, the physical quantity calculation unit 6D is read into the working memory 4C. Then, the physical quantity calculation unit 6D is executed by the calculation unit 4A. FIG. 7 is a flowchart showing an example of the processing procedure of the physical quantity calculation step S5.

In the physical quantity calculation step S5 of the present embodiment, the braking force of the ABS is first calculated (step S51). As described above, in the present embodiment, the braking force of the ABS is the brake torque τ of the above equation (7) of the ABS model. The brake torque τ is _{calculated by multiplying the friction coefficient μ pad} (T) between the disc portion and the pad portion by the pressing force of the pad portion on the disc portion (that is, the brake oil pressure P).

In the first step (at the start of processing) of the first minute time Δt1 in step S51, first, the _{initial value of the reference friction coefficient μ 0} of the pad portion, the initial value of the constant α, and the initial value of the reference temperature T ₀ of the disc portion. , The initial value of the temperature T of the disc part, and the coefficient of friction μ _pad (T) between the disc part and the pad part at the temperature T of the disc part is calculated based on the above equation (8) of the ABS model. Will be done. _{Then, the brake torque τ is calculated based on the friction coefficient μ pad} (T) of the above formula (8), the initial value of the brake oil pressure P, and the above formula (7).

In step S51, after the next step of the first first minute time Δt1, the disc section is based on the temperature T of the new disk section calculated in step S7 described later and the above equation (8) of the ABS model. _{The coefficient of friction μ pad} (T) between the disc portion and the pad portion at the temperature T of is calculated. _{Then, the coefficient of friction μ pad} (T) between the disc portion and the pad portion when the temperature of the disc portion is T, the new brake oil pressure P calculated in the step S7 described later, and the above equation (7) of the ABS model. ), The brake torque τ of the current step of the first minute time Δt1 is calculated.

As described above, in the step S51 of the present embodiment, the braking force (brake torque τ) of the ABS can be calculated while time-developing in the step of the first minute time Δt1. Each physical quantity of ABS including the braking force (brake torque τ) is stored in the physical quantity input unit 5E.

Next, in the physical quantity calculation step S5 of the present embodiment, the tire slip ratio S is calculated (step S52). In step S52, in the first step (at the start of processing) of the first minute time Δt1, the above initial value, the ABS braking force (brake torque τ) calculated by the above equation (7) of the ABS model, and the tire. The slip ratio S is calculated based on the above equations (1) to (3) of the model. The initial values include the initial value of the mass M of the vehicle on which the tire is mounted, the gravity constant g, the initial value of the friction coefficient μ of the tire, the initial value of the moment of inertia I of the tire, the initial value of the tire radius R, and the vehicle body speed V. _{The initial value of the vehicle and} the initial value of the tire speed V _wheel are used.

In step S52, after the next step of the first first minute time Δt1, the above equations (1) to (3) are used based on the new ABS braking force (brake torque τ) calculated in step S51. Therefore, the coefficient of friction μ of the tire in the current step of the first minute time Δt1, the _vehicle body speed V vehicle, the tire speed V _wheel , the slip ratio S, and the like are calculated.

As described above, in the step S52, each physical quantity of the tire including the slip ratio S can be calculated while time-evolving in the step of the first minute time Δt1. Each physical quantity of the tire including the slip ratio S is stored in the physical quantity input unit 5E.

Next, in the simulation method of the present embodiment, the computer 1 calculates the brake oil pressure P (that is, the pressing force of the pad portion on the disc portion) (brake oil pressure calculation step S6). In the brake oil pressure calculation step S6, as shown in FIG. 1, the ABS model stored in the ABS model input unit 5C, the initial value stored in the initial data unit 5A, and stored in the braking force switch input unit 5F. The braking force switch is read into the working memory 4C. Further, the physical quantity calculation unit 6D is read into the working memory 4C. Then, the physical quantity calculation unit 6D is executed by the calculation unit 4A.

In the present embodiment, the current braking force switch (“initial value”, “small” or “large”) set in the step S4 for inputting the initial value to the braking force switch or the braking force changing step S9 described later Based on this, the brake oil pressure P is calculated. FIG. 8 is a flowchart showing an example of the processing procedure of the brake oil pressure calculation step S6.

In the brake oil pressure calculation step S6 of the present embodiment, first, it is determined whether or not the current braking force switch belongs to "initial value", "small", or "large" (step S61).

In step S61, when the current braking force switch is the "initial value", the brake oil pressure P is increased (step S62). In step S62, the brake oil pressure P is increased based on the following equation (12).

ここで、
ＤＴ：第１微小時間Δｔ１
Ｂ：ブレーキ油圧の変化率

here,
DT: First minute time Δt1
B: Rate of change in brake oil pressure

The rate of change (constant) B of the brake oil pressure in the above formula (12) is a positive constant B of the rate of change of the brake oil pressure P for each step of the first minute time Δt1 in the above formula (10). Therefore, in step S62, the brake oil pressure P in the next step (after the first minute time Δt1) can be increased by the above equation (12). As a result, in the simulation method of the present embodiment, the brake torque τ (ABS braking force) of the above formula (7) can be increased in the step S51 (shown in FIG. 7) for calculating the ABS braking force. The brake oil pressure P is described in the physical quantity input unit 5E.

In step S61, when the current braking force switch is "small", the brake oil pressure is reduced (step S63). In step S63, the brake oil pressure P is reduced based on the following equation (13).

ここで、
ＤＴ：第１微小時間Δｔ１
ｄＰ／ｄｔ：ブレーキ油圧の変化率

here,
DT: First minute time Δt1
dP / dt: Rate of change in brake oil pressure

The rate of change dP / dt of the brake oil pressure of the above formula (13) is determined based on the above formula (10). When the braking force switch is "small", it is determined that the tire slip ratio S is larger than the _{tire target slip ratio S 0 in the braking force changing step S9 described later.} Therefore, a negative constant −C of the rate of change of the brake oil pressure P for each step of the first minute time Δt1 is set in dP / dt based on the above equation (10). Therefore, in step S63, the brake oil pressure P in the next step (after the first minute time Δt1) can be reduced by the above equation (13). Thereby, in the simulation method of the present embodiment, the brake torque τ (the braking force of the ABS) of the above formula (7) can be reduced in the step S51 (shown in FIG. 7) for calculating the braking force of the ABS. The brake oil pressure P is stored in the physical quantity input unit 5E.

In step S61, when the current braking force switch is "large", the brake oil pressure P is increased (step S64). In step S64, the brake oil pressure P is increased based on the above formula (13).

The rate of change dP / dt of the brake oil pressure of the above formula (13) is determined based on the above formula (10). When the braking force switch is "small", it is determined that the tire slip ratio S is smaller than the _{tire target slip ratio S 0 in the braking force changing step S9 described later.} Therefore, a positive constant B of the rate of change of the brake oil pressure P for each step of the first minute time Δt1 is set in dP / dt based on the above equation (10). Therefore, in step S64, the brake oil pressure P in the next step (after the first minute time Δt1) can be increased by the above equation (13). As a result, in the simulation method of the present embodiment, the brake torque τ (ABS braking force) of the above formula (7) can be increased in the step S51 (shown in FIG. 7) for calculating the ABS braking force. The brake oil pressure P is stored in the physical quantity input unit 5E.

Next, in the simulation method of the present embodiment, the computer 1 calculates the temperature T of the disk portion (step S7). In step S7, as shown in FIG. 1, the ABS model stored in the ABS model input unit 5C, the initial value stored in the initial data unit 5A, and the disk unit stored in the physical quantity input unit 5E. Temperature T is read into the working memory 4C. Further, the physical quantity calculation unit 6D is read into the working memory 4C. Then, the physical quantity calculation unit 6D is executed by the calculation unit 4A.

In step S7, the temperature T of the disk portion is calculated based on the following formula (14).

ここで、
ｄＴ／ｄｔ：ディスクの温度Ｔの変化率

here,
dT / dt: Rate of change in disk temperature T

The rate of change dT / dt of the temperature T of the disk portion of the above formula (14) is determined based on the above formula (9). As a result, in step S7, the temperature T of the disc is calculated in consideration of the frictional heat generated by the disc portion 13 and the heat dissipation of the disc portion 13. Therefore, in the simulation method of the present embodiment, in the step S51 (shown in FIG. 7) for calculating the braking force of the ABS, the friction coefficient μ _pad (T) between the disc portion and the pad portion of the above formula (8), The brake torque τ (ABS braking force) of the above equation (7) can be calculated accurately. The calculated temperature T of the disk unit is stored in the physical quantity input unit 5E.

Next, in the simulation method of the present embodiment, the computer 1 determines whether or not the current step is the step of the second minute time Δt2 (step S8). The second minute time Δt2 is set to be larger than the first minute time Δt1. The determination in step S8 is executed by the calculation unit 4A (shown in FIG. 1).

In step S8, when it is determined that the current step (step of the first minute time Δt1) is the step of the second minute time Δt2 (“Y” in step S8), the next braking force changing step S9 Will be executed. On the other hand, when it is determined that the current step is not the step of the second minute time Δt2 (“N” in step S8), the step of the first minute time Δt1 is advanced by one (step S10), and the next step is performed. S11 is executed. As described above, the braking force changing step S9 of the present embodiment is executed for each step of the second minute time Δt2.

Next, in the braking force changing step S9, the computer 1 changes the braking force of the ABS of the calculation model based on the physical quantity of the tire. In the braking force changing step S9 of the present embodiment, the braking force switch for controlling whether or not to increase the braking force of the ABS of the calculation model is changed based on the slip ratio S of the tire.

In the braking force changing step S9, as shown in FIG. 1, the μ-S curve function stored in the μ-S curve input unit 5D, the tire slip ratio S stored in the physical quantity input unit 5E, and the tire slip ratio S stored in the physical quantity input unit 5E. , The braking force switch stored in the braking force switch input unit 5F is read into the working memory 4C. Further, the physical quantity calculation unit 6D is read into the working memory 4C. Then, the physical quantity calculation unit 6D is executed by the calculation unit 4A. FIG. 9 is a flowchart showing an example of the processing procedure of the braking force changing step S9.

In the braking force changing step S9 of the present embodiment, first, the current braking force switch is the "initial value", and the tire slip ratio S is the first slip ratio S of the μ-S curve shown in FIG. It is determined whether or not it is between _max and the second slip ratio S _{min (step S91).} The slip ratio S in _{the range between the first slip ratio S max} and the second slip ratio S _min is a region where the tire can be prevented from locking.

In step S91, when it is determined that the current braking force switch is the "initial value" and the current tire slip ratio S is between the first slip ratio S _max and the second slip ratio S _min. (“Y” in step S91), the target slip ratio S ₀ is defined by the current tire slip ratio S (step S92), and the braking force switch is changed to “small” (step S93). The target slip ratio S ₀ is stored in the physical quantity input unit 5E. The braking force switch is stored in the braking force switch input unit 5F.

As described above, in the step S92, the target slip ratio S ₀ is set _{between the first slip ratio S max} and the second slip ratio S _{min, as in the actual ABS.} Further, in step S93, the braking force switch is changed from "initial value" to "small", so that the reduced brake oil pressure P is calculated in the above-mentioned brake oil pressure calculation step S6. As a result, in the step S51 for calculating the braking force of the ABS, the braking force of the small ABS is calculated. Therefore, in step S93, the braking force of ABS can be changed small. Thereby, in the present embodiment, it is possible to prevent the slip ratio S that is increased more than necessary from being calculated in the step S52 (shown in FIG. 7) in which the slip ratio S of the tire is calculated.

On the other hand, in step S91, it is determined that the current braking force switch is not the "initial value" or the current tire slip ratio S is not between _{the first slip ratio S max} and the second slip ratio S _min. If (“N” in step S91), the next step S94 is executed. This makes it possible to prevent the target slip ratio S _{0 from} being defined outside the range between the first slip ratio S _max and the second slip ratio S _min.

Next, in step S94, the computer 1 determines whether or not the current braking force switch is "small" and the current tire slip ratio S is _{smaller than the target slip ratio S 0.} In the general algorithm of ABS (system), when the slip ratio S of the tire _{is smaller than the target slip ratio S 0} , the braking force is increased to prevent the braking distance from becoming long.

In step S94, when it is determined that the current braking force switch is "small" and the current tire slip ratio S is _{smaller than the target slip ratio S 0} ("Y" in step S94), the braking force switch. Is changed to "Large" (step S95). As a result, the increased brake oil pressure P is calculated in the above-mentioned brake oil pressure calculation step S6. Further, in the step S51 for calculating the ABS braking force, a large ABS braking force is calculated. Therefore, in step S95, the braking force of ABS can be significantly changed.

Thereby, in the present embodiment, in the step S52 (shown in FIG. 7) in which the slip ratio S of the tire is calculated, it is possible to prevent the slip ratio S reduced more than necessary from being calculated, and thus the actual ABS. Similarly, it is possible to prevent long braking distances from being calculated. The braking force switch is stored in the braking force switch input unit 5F.

On the other hand, if it is determined in step S94 that the current braking force switch is not "small" or the tire slip ratio S is equal to _{or greater than the target slip ratio S 0} ("N" in step S94), the next step. Step S96 is executed.

Next, in step S96, the computer 1 determines whether or not the current braking force switch is "large" and the current tire slip ratio S is _{larger than the target slip ratio S 0.} In the general algorithm of ABS (system), when the slip ratio S of the tire _{is larger than the target slip ratio S 0} , the braking force is reduced to prevent the tire from locking.

In step S96, when the current braking force switch is "large" and it is determined that the current tire slip ratio S is _{larger than the target slip ratio S 0} ("Y" in step S96), the control The power switch is changed to "small" (step S97). As a result, the reduced brake oil pressure P is calculated in the above-mentioned brake oil pressure calculation step S6. Further, in the step S51 for calculating the braking force of the ABS, the braking force of the small ABS is calculated. Therefore, in step S97, the braking force of ABS can be changed small.

As a result, in the present embodiment, in the step S52 (shown in FIG. 7) in which the tire slip ratio S is calculated, it is possible to prevent the slip ratio S that has increased more than necessary from being calculated, and thus the actual ABS. Similarly, it is possible to prevent the tire lock from being calculated. The braking force switch is stored in the braking force switch input unit 5F.

On the other hand, when the current braking force switch is not "large" or the current tire slip ratio S is determined to be equal to or less than the target slip ratio ("N" in step S96), the next step S10 is carried out. Slip.

As described above, the braking force changing step S9 of the present embodiment is executed for each step of the second minute time Δt2, which is larger than the first minute time Δt1, by the determination of the step S8. In the actual ABS (system), after the braking force is changed (for example, the braking force is "large") in the ABS, and then until the braking force is changed (for example, the braking force is changed to "small"). Takes a certain amount of time. In the simulation method of the present embodiment, the braking force (braking force switch in the present embodiment) is changed in the ABS based on the actual ABS, and then the braking force (braking force switch in the present embodiment) is changed. It is possible to calculate the physical amount of the tire that has received the braking force of ABS in consideration of the time interval (time lag) until the tire is applied. Therefore, the tire braking simulation method of the present invention can accurately calculate the tire braking state when a braking force is applied by ABS.

When the braking force changing step S9 is executed for each step of the second minute time Δt2 which is the same as the first minute time Δt1 as in the conventional simulation method, the slip ratio S is always near the _{target slip ratio S 0.} It is difficult to fully calculate the braking condition of the tire when braking force is applied by ABS.

It is desirable that the second minute time Δt2 is appropriately set based on the characteristics of the ABS and the characteristics of the tire. If the second minute time Δt2 is small, it may be difficult to sufficiently calculate the braking condition of the tire. On the contrary, even if the second minute time Δt2 is large, it becomes larger than the actual time interval (time lag) until the braking force is changed, so that it is difficult to sufficiently calculate the braking condition of the tire. From such a viewpoint, when the first minute time Δt1 is set in the above range, the second minute time Δt2 is preferably 30 times or more, preferably 100 times or less of the first minute time Δt1. Is.

Next, in step S11, the computer 1 _{determines whether or not the vehicle} body speed V vehicle has decreased to a predetermined lower limit value. The determination in step S8 is executed by the calculation unit 4A (shown in FIG. 1). The lower limit value can be appropriately set according to the braking condition of the tire to be calculated by the simulation method of the present embodiment. The lower limit of the present embodiment is set to 30% of the initial value of the _{vehicle body speed V vehicle.}

When it is determined in step S11 that the vehicle body speed V _vehicle has decreased to the lower limit value (“Y” in step S11), a series of processes of the simulation method of the present embodiment is completed. On the other hand, _{when it is determined that the vehicle} body speed V vehicle has not decreased to the lower limit value (“N” in step S11), the physical quantity calculation steps S5 to S11 are executed again. Thereby, the simulation method of the present embodiment can calculate the braking state of the tire when the braking force is applied by ABS until the _{vehicle body speed V vehicle decreases to the lower limit speed.}

Although the particularly preferable embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be modified into various embodiments.

For three types of tires (tire A, tire B, tire C), a calculation model for calculating the braking force of ABS and the physical quantity of the tire subjected to the braking force is available based on the processing procedure shown in FIG. Defined (Examples, Comparative Examples). In the examples and comparative examples, the μ-S curve definition step, the physical quantity calculation step, and the brake oil pressure calculation step were carried out according to the processing procedures shown in FIGS. 5, 7, and 8.

In the embodiment, according to the processing procedure shown in FIG. 9, the braking force of the ABS of the calculation model is changed in the step of the second minute time Δt2, which is larger than the first minute time Δt1, based on the physical quantity of the tire. The process was carried out. _{Further, in the embodiment, the temperature dependence that the friction coefficient μ pad} (T) increases as the temperature T of the disk portion rises by inputting “1.3” to the constant α of the above equation (8) is taken into consideration. Was done. Then, in the embodiment, the average slip ratio, the standard deviation of the slip ratio, and the braking distance of the slip ratio were calculated for the tire A, the tire B, and the tire C.

On the other hand, in the comparative example, the braking force of the ABS of the calculation model was changed in the step of the second minute time Δt2 which is the same as the first minute time Δt1. _{Further, in the comparative example, the temperature dependence of the friction coefficient μ pad} (T) was not taken into consideration because “0” was input to the constant α in the above equation (8). Then, in the comparative example, the average slip ratio, the standard deviation of the slip ratio, and the braking distance were calculated for the tire A, the tire B, and the tire C.

Average when tires A, B, and C are mounted on a domestic FF vehicle with the following mass M under the following conditions _{, traveled at the following vehicle} body speed V vehicle, and the braking force of ABS is applied to the tires for braking. The slip ratio, the standard deviation of the slip ratio, and the braking distance were measured (experimental example (actual vehicle)). The common specifications are as follows.

Tire A, Tire B, Tire C:
Tire size: 195 / 65R15
Rim size: 15 x 6.0 JJ
Internal pressure: 0.2 MPa
initial value:
Vehicle mass M: 250 kg
Gravitational constant g: 9.8 m / s ²
Tire friction coefficient μ: 0.1
Moment of inertia of tire I: 0.6kg ・ m ²
Tire radius R: 0.31m
Body speed V _vehicle : 27.8m / s (100km / h)
Tire speed V _wheel : 27.8m / s
Disk temperature T: 25 ° C
Reference friction coefficient of pad part μ ₀ : 1.0
Outside temperature T _atm : 25 ° C
Reference temperature of the disk part T ₀ : 25 ° C
Constant A: 100
Constant B: 10
Constant C: 25
Constant D: 1
Constant E: 0.2
First minute time Δt1: 0.0001s
Second minute time Δt2:
Example: 0.005s (ie, Δt2 = Δt1 × 50)
Comparative example: 0.0001s (that is, Δt2 = Δt1)
Lower limit of speed (simulation end condition): 8.34 m / s

FIG. 10 is a graph showing the relationship between the average slip ratio of the simulations of Examples and Comparative Examples and the average slip ratio of Experimental Examples. FIG. 11 is a graph showing the relationship between the standard deviation of the slip ratio of the simulations of the examples and the comparative examples and the standard deviation of the slip ratio of the experimental example. FIG. 12 is a graph showing the relationship between the braking distances of the simulations of Examples and Comparative Examples and the braking distances of Experimental Examples. As is clear from FIGS. 10 to 12, the examples were closer to the slip ratio and the braking distance of the experimental examples as compared with the comparative examples. Therefore, in the example, the braking state of the tire when the braking force was applied by ABS could be calculated more accurately than in the comparative example.

S1 Step to define the calculation model S5 Step to calculate the physical quantity of the tire S9 Step to change the braking force of ABS

Claims (5)

It is a method for calculating the braking state of the tire when a braking force is applied to the tire traveling on the road surface by ABS, using a computer.
The computer includes a step of defining a calculation model for calculating the braking force of the ABS and the physical quantity of the tire subjected to the braking force.
The computer
Using the calculation model, the step of calculating the physical quantity of the tire while time-evolving in the step of the first minute time Δt1 and
A tire braking simulation method for executing a step of changing the braking force of the ABS of the calculation model in a step of a second minute time Δt2 larger than the first minute time Δt1 based on the physical quantity of the tire. .. The step of calculating the physical quantity includes a step of calculating the slip ratio of the tire.
The step of changing the braking force of the ABS is
A step of reducing the braking force of the ABS when the slip ratio of the tire is larger than a predetermined target slip ratio.
The tire braking simulation method according to claim 1, further comprising a step of increasing the braking force of the ABS when the tire slip ratio is smaller than the target slip ratio. Prior to the step of changing the braking force of the ABS, a step of inputting a μ-S curve showing the relationship between the friction coefficient μ of the tire and the slip ratio S into the computer,
The target slip ratio is defined between the first slip ratio at which the friction coefficient μ of the μ-S curve is maximized and the second slip ratio at which the friction coefficient μ of the μ-S curve is minimized. The tire braking simulation method according to claim 2, further comprising a step. The ABS includes a disc portion that rotates with the tire and a pad portion that contacts the disc portion.
The step of calculating the physical quantity further includes a step of calculating the braking force by multiplying the friction coefficient between the disc portion and the pad portion by the pressing force of the pad portion on the disc portion. The tire braking simulation method according to any one of claims 1 to 3. The tire braking simulation method according to claim 4, wherein the coefficient of friction between the disc portion and the pad portion is defined as a temperature dependence that increases as the temperature of the disc portion rises.

Images