JP2022160933A - Device for estimating abrasion state of tire - Google Patents

Abstract

To precisely estimate an abrasion state of a tire while taking an influence of temperature into consideration.SOLUTION: A device comprises a rotation speed acquisition part, a drive force acquisition part, a temperature acquisition part, a slip ratio calculation part, an inclination calculation part, an inclination correction part, and an estimation part. The rotation speed acquisition part acquires rotation speeds of tires mounted on a vehicle one after another. The drive force acquisition part acquires drive force of the vehicle one after another. The temperature acquisition part acquires the temperature outside the vehicle. The slip ratio calculation part calculates a slip ratio based upon the rotation speeds of the tires acquired one after another. The inclination calculation part calculates an inclination of the slip ratio to the drive force as a regression coefficient representing linear relation between the slip ratio and drive force based upon many data sets of slip ratios and drive force. The inclination correction part corrects the calculated inclination based upon an index representing temperature dependency of the inclination and temperature at the time of the correction. The estimation part estimates wear states of the tires based upon the corrected inclination.SELECTED DRAWING: Figure 3

Description

The present invention provides a device for estimating the state of wear of a tire mounted on a vehicle, a determination device for determining the state of a road surface on which a vehicle travels, a method for estimating the state of tire wear, a method for determining the state of a road surface, and a method for determining the state of a road surface. The present invention relates to a program for estimating the state of wear and a program for determining the state of a road surface.

Patent Literature 1 discloses a device capable of determining the condition of a road surface and determining the wear condition of a tire. According to the device disclosed in Patent Document 1, the inclination of the relational expression between the slip ratio calculated from the wheel speed of the tire and the acceleration/deceleration of the vehicle is used as the judgment value of the road surface, and the judgment value is compared with a predetermined threshold value. By doing so, the road surface condition is determined. The threshold value is changed by a formula stored in advance in the device according to the type of tire read from the wireless ID tag of the tire. The wear state of the tire is also estimated by comparing the changed threshold with the average value of the determination values during asphalt running.

Japanese Patent Application Laid-Open No. 2005-138702

Patent Document 1 describes that when a tire wears, the stiffness of the tread increases and the determination value for determining the slipperiness of the road surface decreases. Here, the stiffness also changes depending on the temperature. However, Patent Document 1 does not consider the influence of temperature on the judgment value for judging the slipperiness of the road surface. For this reason, as in Patent Document 1, in control using a determination value that depends on stiffness, particularly a value based on the slope of a regression line between slip ratio and acceleration/deceleration (driving force), there is a risk of deterioration in accuracy due to the influence of temperature. There is

The present invention provides a device, method, and program capable of accurately estimating the state of wear of a tire, taking into account the influence of temperature, and a device, method, and program capable of accurately determining the state of a road surface. intended to

A device according to a first aspect of the present invention is a device for estimating the wear state of a tire mounted on a vehicle, comprising a rotational speed acquisition unit, a driving force acquisition unit, a temperature acquisition unit, and a slip ratio calculation unit. , a slope calculator, a slope corrector, and an estimator. The rotational speed obtaining unit sequentially obtains rotational speeds of tires mounted on the vehicle. The driving force acquiring unit sequentially acquires the driving force of the vehicle. The temperature acquisition unit acquires the temperature outside the vehicle. The slip ratio calculator calculates a slip ratio based on the rotational speed of the tire that is sequentially obtained. The slope calculator calculates the slope of the slip ratio with respect to the driving force, as a regression coefficient representing a linear relationship between the slip ratio and the driving force, based on a large number of data sets of the slip ratio and the driving force. . The tilt correction unit corrects the calculated tilt based on an index representing the temperature dependence of the tilt and the temperature at the time of correction. The estimator estimates the wear state of the tire based on the corrected tilt.

A device according to a second aspect of the present invention is a device for determining the state of a road surface on which a vehicle travels, comprising a rotation speed acquisition unit, a driving force acquisition unit, a temperature acquisition unit, a slip ratio calculation unit, an inclination A calculation unit, an inclination correction unit, and a determination unit are provided. The rotational speed obtaining unit sequentially obtains rotational speeds of tires mounted on the vehicle. The driving force acquiring unit sequentially acquires the driving force of the vehicle. The temperature acquisition unit acquires the temperature outside the vehicle. The slip ratio calculator calculates a slip ratio based on the rotational speed of the tire that is sequentially obtained. The slope calculator calculates the slope of the slip ratio with respect to the driving force, as a regression coefficient representing a linear relationship between the slip ratio and the driving force, based on a large number of data sets of the slip ratio and the driving force. . The tilt correction unit corrects the calculated tilt based on an index representing the temperature dependence of the tilt and the temperature at the time of correction. The determination unit determines the state of the road surface based on the corrected tilt.

A device according to a third aspect of the present invention is the device according to the first aspect or the second aspect, wherein the index is a slope representing a linear relationship between the temperature and the slope.

A device according to a fourth aspect of the present invention is the device according to any one of the first aspect to the third aspect, further comprising a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle. The slip ratio calculator calculates the slip ratio of the tire based on the rotational speed of the left tire among the rotational speeds of the tires that are sequentially obtained according to the lateral acceleration that is sequentially obtained. A first slip ratio, a second slip ratio that is the slip ratio of the tire calculated based on the rotational speed of the right tire, and a slip ratio of the tire that is calculated based on the average rotational speed of the left and right tires. Any one of the group including the third slip ratio is sequentially selected and obtained.

A device according to a fifth aspect of the present invention is the device according to the fourth aspect, wherein the slip ratio calculator calculates the first slip ratio when the vehicle turns right according to the lateral acceleration. The second slip ratio is selected when the vehicle is turning left, and the third slip ratio is selected when the vehicle is traveling straight.

A device according to a sixth aspect of the present invention is the device according to any one of the first aspect to the fifth aspect, comprising: a turning radius obtaining unit for obtaining a turning radius of the vehicle; and a first correction unit that corrects the slip ratio based on the turning radius at the time of correction.

A device according to a seventh aspect of the present invention is the device according to the sixth aspect, wherein the first relational information is information representing the slip ratio as a quadratic function of the reciprocal of the turning radius.

A device according to an eighth aspect of the present invention is the device according to any one of the first aspect to the seventh aspect, comprising: a lateral acceleration acquisition unit configured to sequentially acquire lateral acceleration applied to the vehicle; and second relational information representing the relationship between the driving force and the slip ratio, and a second correcting unit that corrects the slip ratio based on the lateral acceleration and the driving force at the time of correction.

A device according to a ninth aspect of the present invention is the device according to the eighth aspect, wherein the second relational information represents the slip ratio as a linear function of the driving force, and the slope of the slip ratio with respect to the driving force is expressed as a quadratic function of the lateral acceleration.

A method according to a tenth aspect of the present invention is a method of estimating the state of wear of a tire mounted on a vehicle, and includes the following. A program according to a twelfth aspect of the present invention is a program for estimating wear states of tires mounted on a vehicle, and causes a computer to execute the following.
- To sequentially acquire the rotation speed of the tires mounted on the vehicle.
- Obtaining the driving force of the vehicle sequentially.
- Obtaining the temperature of the exterior of the vehicle.
• Calculating a slip ratio based on the rotational speed of the tire that is obtained sequentially.
• Calculating the slope of the slip ratio with respect to the driving force based on multiple data sets of the slip ratio and the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force.
- Correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction.
- estimating the state of wear of the tire based on the corrected inclination;

A method according to an eleventh aspect of the present invention is a method for determining the state of a road surface on which a vehicle travels, and includes the following. A program according to a thirteenth aspect of the present invention is a program for determining the state of a road surface on which a vehicle travels, and causes a computer to execute the following.
- To sequentially acquire the rotation speed of the tires mounted on the vehicle.
- Obtaining the driving force of the vehicle sequentially.
- Obtaining the temperature of the exterior of the vehicle.
• Calculating a slip ratio based on the rotational speed of the tire that is obtained sequentially.
• Calculating the slope of the slip ratio with respect to the driving force based on multiple data sets of the slip ratio and the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force.
- Correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction.
- Determining the condition of the road surface based on the corrected inclination.

A value based on the slope of the relational expression between the slip ratio and the driving force (acceleration/deceleration) of the vehicle is used as an index for determining whether the tire easily slips on the road surface. This index is also related to the driving stiffness of the tire, and changes depending on the slipperiness of the road surface on which the vehicle travels and the degree of wear of the tire. Since driving stiffness is also affected by temperature, the slope of the relational expression between the slip ratio and the driving force (acceleration/deceleration) of the vehicle also changes depending on the temperature. According to a first aspect of the present invention, slope-based values corrected for temperature effects are used for estimating the state of tire wear. This makes it possible to more accurately estimate the wear state of the tire. Further, according to the second aspect of the present invention, a value based on the slope corrected for the influence of temperature is used for determining the state of the road surface. This makes it possible to more accurately determine the state of the road surface on which the vehicle is traveling.

FIG. 2 is a schematic diagram showing a state in which a control unit as an estimation device according to the first embodiment is mounted on a vehicle; FIG. 2 is a block diagram showing the electrical configuration of the control unit according to the first embodiment; FIG. 4 is a flowchart showing the flow of wear state estimation processing according to the first embodiment; A graph showing the relationship between the slip ratio and the turning radius of the vehicle. 4 is a graph showing the relationship between the slope of the slip ratio with respect to the driving force and the lateral acceleration; 4 is a graph showing the relationship between slip ratio and driving force; The graph which plotted the braking force coefficient and slip ratio which were acquired by experiment. The graph which plotted the braking force coefficient and slip ratio which were acquired by experiment. Graph plotting driving force and slip ratio obtained by experiment. Graph plotting driving force and slip ratio obtained by experiment. A graph showing the temperature dependence of the slope. A graph showing the temperature dependence of the slope. A graph showing the temperature dependence of the slope. A graph showing the temperature dependence of the slope. The block diagram which shows the electrical structure of the control unit which concerns on 2nd Embodiment. FIG. 11 is a flow chart showing the flow of road surface state determination processing according to the second embodiment; FIG. Graph showing the relationship between various slip ratios and driving force when traveling straight, turning left, and turning right. 4 is a graph showing the relationship between the first slip ratio, the second slip ratio, and the driving force for various vehicle body speeds when traveling straight. 5 is a graph showing the relationship between the first slip ratio, the second slip ratio, and the driving force for various vehicle body speeds during left turning; 4 is a graph showing the relationship between the first slip ratio, the second slip ratio, and the driving force for various vehicle body speeds during right turning. The graph which compares the strength of the correlation of the slope with respect to the degree of wear with and without correction. The graph which compares the strength of the correlation of the slope with respect to the degree of wear with and without correction.

Hereinafter, devices, methods, and programs according to some embodiments of the present invention will be described with reference to the drawings.

<1. First Embodiment>
<1-1. Configuration of device for estimating wear state>
FIG. 1 is a schematic diagram showing a state in which a control unit 2 as a device (estimating device) for estimating the wear condition of a tire according to the first embodiment is mounted on a vehicle 1. As shown in FIG. The vehicle 1 is a four-wheeled vehicle and includes a front left wheel FL, a front right wheel FR, a rear left wheel RL and a rear right wheel RR. Tires T _FL , T _FR , T _RL , and T _RR are attached to the wheels FL, FR, RL, and RR, respectively. The vehicle 1 according to the present embodiment is a front-engine, front-drive vehicle (FF vehicle) in which the front tires T _FL and T _FR are drive tires, and the rear tires T _RL and T _RR are driven tires. .

The control unit 2 determines the slip easiness of the running tires T _FL , T _FR , T _RL , and T _RR based on the information on the rotational speed of the running tires T _FL , T _FR , T _RL , and T _RR . is determined, and based on the slope of the slip ratio S with respect to the driving force F of the vehicle 1, the average wear state of the tires _TFL and _TFR , which are driving wheel tires, is estimated. Grooves formed in the tread portion of a tire become shallower as it wears. As a result, the tires are more likely to slip, which in turn leads to a decrease in driving force and braking force. In order to prevent such a situation from becoming more serious, it is generally recommended to replace the tire when the depth of the tread groove becomes equal to or less than a predetermined threshold value. The control unit 2 estimates the average depth of remaining grooves of the tires T _FL and T _FR as the worn state of the tires T _FL and T _FR , detects the timing at which tire replacement is recommended, and informs the driver of the vehicle 1 of this. to notify.

The information on the tire wear state can be applied to various purposes other than prompting the driver of the vehicle 1 to timely replace the tire. Information on tire wear can be applied, for example, to monitoring the slipperiness of road surfaces and controlling brake systems.

Wheel speed sensors 6 are attached to the tires T _FL , T _FR , T _RL , and T _RR (more precisely, the wheels FL, FR, RL, and RR) of the vehicle 1, and the wheel speed sensors 6 are , and detects the rotation speeds of the tires (that is, the wheel speeds) V1 to V4 mounted on the wheels on which it is mounted. V1 to V4 are the rotational speeds of the tires T _FL , T _FR , T _RL and T _RR respectively. As the wheel speed sensor 6, any sensor can be used as long as it can detect the wheel speed of the wheels FL, FR, RL, and RR during running. For example, it is possible to use a sensor that measures the wheel speed from the output signal of an electromagnetic pickup, or a sensor that generates electricity using rotation like a dynamo and measures the wheel speed from the voltage at this time. can also be used. The mounting position of the wheel speed sensor 6 is also not particularly limited, and can be appropriately selected according to the type of sensor as long as the wheel speed can be detected. A wheel speed sensor 6 is connected to the control unit 2 via a communication line 5 . Information on the rotational speeds V1 to V4 detected by the wheel speed sensors 6 is transmitted to the control unit 2 in real time.

A torque sensor 7 for detecting a wheel torque WT of the vehicle 1 is attached to the vehicle 1 . As long as the torque sensor 7 can detect the wheel torque WT of the vehicle 1, its structure and mounting position are not particularly limited. Torque sensor 7 is connected to control unit 2 via communication line 5 . Information on the wheel torque WT detected by the torque sensor 7 is sent to the control unit 2 in real time, as is the information on the rotational speeds V1 to V4.

Further, the vehicle 1 is equipped with a lateral acceleration sensor 4 for detecting lateral acceleration γ applied to the vehicle 1 . The lateral acceleration γ is centrifugal acceleration that acts on the vehicle 1 toward the outside of the turn when the vehicle 1 turns. As long as the lateral acceleration sensor 4 can detect the lateral acceleration γ, its structure and mounting position are not particularly limited. A lateral acceleration sensor 4 is connected to the control unit 2 via a communication line 5 . Information on the lateral acceleration γ detected by the lateral acceleration sensor 4 is sent to the control unit 2 in real time, as is information on the rotational speeds V1 to V4 and the acceleration α.

A yaw rate sensor 8 for detecting a yaw rate ω of the vehicle 1 is attached to the vehicle 1 . The yaw rate ω is the rotational angular velocity about the vertical axis when the vehicle 1 turns. As the yaw rate sensor 8, for example, a sensor that detects the yaw rate using the Coriolis force can be used. A yaw rate sensor 8 is connected to the control unit 2 via a communication line 5 . Information on the yaw rate ω detected by the yaw rate sensor 8 is sent to the control unit 2 in real time, as is information on the rotational speeds V1 to V4, the acceleration α and the lateral acceleration γ.

A temperature sensor 9 for detecting the temperature outside the vehicle 1 is attached to the vehicle 1 . Any temperature sensor can be used as the temperature sensor 9 as long as it can detect the temperature outside the vehicle 1. For example, a thermistor, a semiconductor, a thermocouple, or the like can be used. be able to. Although the mounting position of the temperature sensor 9 is not particularly limited, it is preferably a position that is not easily affected by the heat of the engine of the vehicle 1 or the exhaust gas. A temperature sensor 9 is connected to the control unit 2 via a communication line 5 . Information on the external temperature detected by the temperature sensor 9 is sent to the control unit 2 in real time, as is information on the rotational speeds V1 to V4, wheel torque WT, lateral acceleration γ and yaw rate ω.

FIG. 2 is a block diagram showing the electrical configuration of the control unit 2. As shown in FIG. The control unit 2 is a computer mounted on the vehicle 1, and as shown in FIG. The I/O interface 11 is a communication device for communicating with external devices such as the wheel speed sensor 6, the torque sensor 7, the lateral acceleration sensor 4, the yaw rate sensor 8, the temperature sensor 9, and the display 3. A ROM 13 stores a program 10 for controlling the operation of each part of the vehicle 1 . By reading and executing the program 10 from the ROM 13, the CPU 12 virtually obtains the rotation speed acquisition unit 21, the driving force acquisition unit 22, the lateral acceleration acquisition unit 23, the turning radius acquisition unit 24, the temperature acquisition unit 25, the slip ratio It operates as a calculation unit 26 , a relationship identification unit 27 , a correction unit 28 , an inclination calculation unit 29 , an inclination correction unit 30 and an estimation unit 31 . The correction section 28 is an example of the first correction section and the second correction section of the present invention. Details of the operations of the units 21 to 31 will be described later. The storage device 15 is composed of a hard disk, a flash memory, or the like. The storage location of the program 10 may be the storage device 15 instead of the ROM 13 . The RAM 14 and the storage device 15 are appropriately used for calculation of the CPU 12 .

The display device 3 can output various information including warnings to the user (mainly the driver), and can be realized in any form such as a liquid crystal display element, a liquid crystal monitor, a plasma display, an organic EL display, etc. . The mounting position of the display device 3 can be selected as appropriate, but it is preferable to provide it at a position that is easily recognized by the driver, such as on the instrument panel. When the control unit 2 is connected to a car navigation system, it is possible to use a monitor for car navigation as the display 3 . When a monitor is used as the display 3, the alarm can be an icon or character information displayed on the monitor.

<1-2. Estimation Processing of Wear State>
An estimation process for calculating a regression coefficient between the driving force F and the slip ratio S of the vehicle 1 and estimating the state of tire wear based on the regression coefficient will be described below with reference to FIG. This estimation process may be repeatedly performed while the electric system of the vehicle 1 is powered on, or may be performed at a predetermined frequency such as once a day while the vehicle 1 is running. good too.

In step S1, the rotation speed acquisition unit 21 acquires the rotation speeds V1 to V4 of the running tires T _FL , T _FR , T _RL and T _RR . The rotational speed acquisition unit 21 receives output signals from the wheel speed sensor 6 in a predetermined sampling cycle and converts them into rotational speeds V1 to V4.

In step S<b>2 , the driving force acquisition unit 22 acquires the wheel torque WT of the vehicle 1 . The driving force acquisition unit 22 receives an output signal from the torque sensor 7 in a predetermined sampling period and converts it into wheel torque WT.

Here, it may be determined whether the process proceeds to step S3 depending on whether the data of the rotational speeds V1 to V4 and the wheel torque WT acquired in steps S1 and S2 are valid data. Valid data is data that can be used to accurately estimate the state of wear in subsequent processing, and ineffective data is data that can have an undesirable effect on estimation of the state of wear. Examples of data that are not valid include, for example, data acquired during braking of the vehicle 1 . In this embodiment, when the data of the rotational speeds V1 to V4 and the wheel torque WT obtained in steps S1 and S2 are determined to be valid data, the process proceeds to step S3. On the other hand, when it is determined that the data of the rotation speeds V1 to V4 and the wheel torque WT are not valid data, the data are discarded and the process returns to step S1.

In step S<b>3 , the lateral acceleration acquisition unit 23 acquires the lateral acceleration γ applied to the vehicle 1 . The lateral acceleration acquisition unit 23 receives an output signal from the lateral acceleration sensor 4 in a predetermined sampling cycle and converts it into lateral acceleration γ.

In step S<b>4 , the turning radius acquisition unit 24 acquires the yaw rate ω of the vehicle 1 . A turning radius acquisition unit 24 receives an output signal from the yaw rate sensor 8 in a predetermined sampling period and converts it into a yaw rate ω. The turning radius acquisition unit 24 acquires the turning radius R of the vehicle 1 by dividing the vehicle body speed by the yaw rate ω. Since the vehicle body speed can be approximated by the speed of the driven wheels, it can also be calculated as R=(V3+V4)/2ω, for example.

In step S<b>5 , the temperature acquisition unit 25 acquires the temperature T outside the vehicle 1 . The temperature acquisition unit 25 receives an output signal from the temperature sensor 9 in a predetermined sampling cycle and converts it into a temperature T.

In step S6, the driving force acquisition unit 22 calculates the driving force F of the vehicle 1 from the converted wheel torque WT. The driving force F can be calculated, for example, by dividing the wheel torque WT by the radii of the tires T _FL , T _FR , T _RL and T _RR .

At step S7, the slip ratio calculator 26 calculates the slip ratio S based on the rotation speeds V1 to V4. In this embodiment, the slip ratio S is calculated as (drive wheel speed−vehicle speed)/vehicle speed, and the speed of the driven wheels is used as the vehicle speed. The slip ratio S is defined as follows in this embodiment.
S={(V1+V2)−(V3+V4)}/(V3+V4)

After steps S6 and S7 are executed and before the next process is executed, for the driving force F of the vehicle 1 calculated in step S6 and the slip ratio S calculated in step S7, Filtering may be performed to remove measurement errors.

The rotational speeds V1 to V4, wheel torque WT, lateral acceleration γ, yaw rate ω, turning radius R, temperature T, slip ratio S, and driving force F obtained in steps S1 to S7 that are continuously executed are: , are handled as a data set acquired at the same time or approximately at the same time, and stored in the RAM 14 or the storage device 15 . As shown in FIG. 3, steps S1 to S7 are repeatedly executed, so the above data sets are obtained sequentially. After step S7, when N1 (N1≧2) such data sets are collected, the process proceeds to steps S8 and S9. Steps S8 and S9 are executed only once. After steps S8 and S9 are executed once, the process proceeds to step S10 after steps S1 to S7.

In step S8, the relationship identifying unit 27 determines the relationship between the turning radius R and the slip ratio S based on a large number of data sets of the turning radius R calculated in step S4 and the slip ratio S calculated in step S7. Identify the first relationship information representing The first relational information is used for subsequent correction of the slip ratio S (step S10). In this embodiment, the wear state is estimated based on the linear relationship between the slip ratio S and the driving force F. However, when the vehicle 1 is turning, even if the vehicle 1 is traveling on the same road surface, the linear relationship between the slip ratio S and the driving force F changes compared to when the vehicle 1 is traveling straight ahead, so the wear condition can be correctly estimated. can become impossible. This is because a track difference (path difference) occurs between the left and right tires during turning, and the slip ratio S changes from when the vehicle is traveling straight due to the influence of this track difference. Therefore, here, in order to realize various types of stable control based on the slip ratio S, the slip ratio S cancels the influence caused by the difference between the left and right trajectories during turning.

The difference between the left and right trajectories during turning depends on the turning radius R, and a certain relationship is established between the turning radius R and the slip ratio S. According to experiments conducted by the present inventor, the slip ratio S is generally represented by a quadratic function of the reciprocal of the turning radius R, as shown in FIG. 4A. _In step S8, the relationship specifying unit 27 specifies the coefficients a1, _b1 and c1 of the following equation as the _first relationship information representing the relationship between the turning radius R and the slip ratio S.
S=a1( ₁ /R) ² +b1( _{1 /} R)+c1

The coefficients a ₁ , b ₁ and c ₁ are calculated based on a large number of data sets of the slip ratio S and the turning radius R stored in the RAM 14 or the storage device 15, for example, by a method such as the least squares method. be.

The apex of the parabola representing the relationship between the reciprocal of the turning radius R and the slip ratio S corresponds to straight running, and substantially overlaps the vertical axis representing the slip ratio S as shown in FIG. In other words, b ₁ is approximately zero. Therefore, here, only the coefficients a ₁ and c ₁ can be specified as the first relational information according to the following formula.
S=a1( _{1 /} R) ² +c1

In step S9, the relationship identifying unit 27 determines the lateral acceleration γ, the driving force F, and the slip ratio based on the multiple data sets of the lateral acceleration γ, the slip ratio S, and the driving force F obtained in step S23. The second relationship information representing the relationship with S is specified. The second relational information is also used for subsequent correction of the slip ratio S (step S11). As described above, while the vehicle 1 is turning, the linear relationship between the slip ratio S and the driving force F changes, so it may not be possible to correctly estimate the wear state. Then, during turning, this linear relationship changes from that when traveling straight due not only to the difference between the left and right tracks, but also to the influence of the load shift in the left and right directions of the vehicle body. This is because the slip ratio S changes from when the vehicle travels straight due to the influence of such load movement. Therefore, here, in order to realize various types of stable control based on the slip ratio S, the slip ratio S cancels the influence caused by the lateral load movement during turning.

The lateral load movement during turning depends on the lateral acceleration γ, and a certain relationship is established between the lateral acceleration γ and the slope f1 of the slip ratio S with respect to the driving force F. According to experiments conducted by the present inventor, the slope f1 is generally represented by a quadratic function of the lateral acceleration γ, as shown in FIG. 4B. In step S9, the relationship specifying unit 27 obtains the coefficients _a2 , _b2 , c2 and f2 of the following equation as the _second relationship information representing the relationship between the lateral acceleration γ, the driving force F and the slip ratio S. identify. Note that f2 is the intercept of the slip ratio S with respect to the driving force F.
S=f1F+f2=(a2γ2 _{+ b2γ} ⁺ c2)F ₊ f2

The coefficients a ₂ , b ₂ , c ₂ and f2 are calculated based on multiple data sets of the slip ratio S, the driving force F and the lateral acceleration γ, and are calculated by methods such as the least squares method. Further, the range of the lateral acceleration γ is divided into arbitrary ranges, linear regression is performed on the slip ratio S and the driving force F in each range, and regression coefficients f1 and f2 are calculated. It is also possible to calculate the average value and the average value of the slope f1, and to specify the coefficients a ₂ , b ₂ and c ₂ based on these average values by Gaussian elimination.

When step S9 ends, the process returns to step S1, and steps S1 to S7 are repeated again. As shown in FIG. 3, steps S8 and S9 are executed once, and the first relational information a ₁ , b ₁ and c ₁ between the turning radius R and the slip ratio S, the lateral acceleration γ, the driving force F and the slip ratio S After the second relational information a ₂ , b ₂ and c ₂ with are specified, steps S10 to S13 are repeatedly performed each time steps S1 to S7 are performed once.

_In step S10, the correcting unit 28 _{generates a} , correct the latest slip ratio S obtained in step S7. As described above, the slip ratio S is represented by a quadratic function of the reciprocal of the turning radius R. Therefore, the correction unit 28 corrects the slip ratio S by subtracting from the slip _ratio S the value obtained by multiplying the reciprocal of the corrected turning radius R squared by the coefficient a1 according to the following equation.
S=Sa ₁ (1/R) ²
Note that the slip ratio S may be corrected by further subtracting from the slip ratio S a value obtained by multiplying the reciprocal of the turning radius R at the time of correction by _a coefficient b1, using the following equation.
S=Sa ₁ (1/R) ² -b ₁ (1/R)

According to the above correction formula, as shown in FIG. 4A, when (1/R) is substantially equal to 0, that is, when the vehicle is traveling straight ahead, the slip ratio S can be calculated. And the influence of the trajectory difference due to the right turn is cancelled.

In the next step S11, the correction unit 28 obtains the _second relational information _a2 , _b2 , and c2 representing the relationship between the lateral acceleration γ and the slip ratio S, and the latest lateral acceleration γ obtained in step S3. and the latest driving force F obtained in step S6, the slip ratio S obtained in step S10 is further corrected. As described above, the slip ratio S is represented by a linear function of the driving force F with the slope f1, and the slope f1 is represented by a quadratic function of the lateral acceleration γ. Therefore, according to the following formula, the correction unit 28 obtains a value obtained by multiplying the square of the corrected lateral acceleration γ by a coefficient a ₂ , a value obtained by multiplying the corrected lateral acceleration γ by a coefficient b ₂ , and c ₂ , the product of the sum and the driving force F at the time of correction is calculated, and the product is subtracted from the slip ratio S acquired in step S10, thereby further correcting the slip ratio S.
S=S−f1F=S−(a ₂ γ ² +b ₂ γ+c ₂ )F

Since b ₂ is also approximately 0, the slip ratio S may be corrected according to the following equation.
S=S−(a ₂ γ ² +c ₂ )F

According to the above correction formula, it is possible to calculate the slip ratio S in terms of straight running, and from the slip ratio S, the influence of the load shift in the left-right direction due to left and right turns is canceled.

In step S12, the slope calculator 29 calculates a regression coefficient representing a linear relationship between the driving force F and the slip ratio S based on a large number of data sets of the driving force F and the corrected slip ratio S. A slope f1 and an intercept f2 of the slip ratio S are calculated. The slope f1 and the intercept f2 can be calculated by, for example, the method of least squares. The slope f1 and the intercept f2 may be calculated sequentially based on multiple data sets of the driving force F and the slip ratio S, or may be calculated by batch processing. In this embodiment, the iterative least-squares method is used as a preferred example.

By the way, in order to calculate an appropriate slope f1 and intercept f2, it is preferable that the data of the driving force F in a predetermined period have a certain amount or more of variation. However, during a period in which the driving force F does not change much, such as a period in which the vehicle 1 is running at a constant speed on a downward slope, the data sets show little variation. Therefore, at the time of estimating the wear state, it is determined whether or not the variation in the driving force F is greater than or equal to a certain value. f1 and intercept f2 may be calculated. The variation in the driving force F can be determined, for example, by the width and variance of the driving force F acquired in the most recent predetermined period. can be determined to exist.

In subsequent steps, the wear state of the tire is estimated based on the corrected slope f1 of the slip ratio S. However, as will be explained below, the slope f1 also depends on the ambient temperature. Therefore, an index indicating the degree of change in the slope f1 with respect to the difference between the acquired temperature T and the reference temperature T1 is specified in advance by simulation or experiment, and the slope f1 is corrected in step S13 based on the specified index. be done. First, the principle of estimating the state of wear from the slope f1 of the slip ratio S will be described.

Generally, it is known that the relationship shown in the graph of FIG. 5 holds between the slip ratio S and the driving force F when the road surface condition is constant. However, in the graph of FIG. 5, the slip ratio S is plotted on the horizontal axis, and the driving force F is plotted on the vertical axis. Under the environment in which the vehicle 1 normally travels, the slip ratio S generally transitions within the range of 0 to Sc. As can be seen from FIG. 5, in the region where the slip ratio S is 0 to Sc, it can be said that an approximate linear relationship exists between the slip ratio S and the driving force F, and this approximate linear relationship dominates. Driving stiffness represented by the following formula (1) is known as one of the important factors.
C=wk _× l ² /2 (1)

Here, w is the contact width of the tire, k _x is the shear stiffness per unit area of the tread rubber block TB (hereinafter also referred to as block TB) of the tire, and l is the contact length of the tire. Assume that the block TB is a rectangular parallelepiped.

From equation (1), it is considered that the slope f1 of the slip ratio S with respect to the driving force F decreases as the shear stiffness k _x per unit area of the block TB increases. Therefore, it is assumed that the slope f1 is inversely proportional to the shear stiffness _kx per unit area. On the other hand, the shear stiffness _kx per unit area of the block TB is said to increase as the wear progresses. That is, if the conditions of the road surface are constant, it is considered that the slope f1 becomes smaller as the wear progresses.

The inventor conducted an experiment to prove the above. 6 and 7 are graphs showing the respective experimental results. First, the inventor measured the braking force coefficient μ with respect to the tire slip ratio S using tires of the same type with wear amounts W of 0 mm (no wear), 2 mm, 4 mm, and 6 mm. Here, the wear amount W is the amount obtained by subtracting the depth of the groove of the current tire from the depth of the groove of the new tire. This measurement was carried out under the same dry asphalt conditions for each tire, using dedicated laboratory equipment for measuring μ-S characteristics. The results are the graphs shown in FIGS. 6A and 6B. The graph of FIG. 6B details the range of the slip ratio S from 0 to 0.1 of the graph of FIG. 6A. As can be seen from FIGS. 6A and 6B, as the amount of wear W increased, the braking force coefficient μ increased for the same slip ratio S. From this, it was confirmed that the shear rigidity k _x per unit area of the block TB increases as the wear amount W increases. Then, as described above, since the slope f1 is inversely proportional to the shear stiffness k _x per unit area, it is considered that the slope f1 decreases as the wear amount W increases.

Therefore, the inventor conducted a further experiment in order to prove that the inclination f1 becomes smaller as the amount of wear W increases. Figures 7A and 7B are graphs representing the results of this experiment. In the experiment, the slope f1 is calculated when the vehicle is driven straight with new tires (W=0) on the four wheels and when the vehicle is driven straight with worn tires on the four wheels. It was done by The same vehicle was used, and the road surface was the same dry asphalt road surface. The slope f1 was calculated using the output signal of a sensor mounted on the vehicle in the same procedure as in step S12, which will be described later. The graph in FIG. 7A plots the driving force F and the slip ratio S when running on new tires, and the driving force F and slip ratio S when running on the same type of worn tires (W = 6 mm). It is what I did. When the regression coefficient was calculated for each data set of the tire in the new condition and the worn condition, the slope f1 in the worn condition was 0.0183, which was smaller than the slope f1 _N (=0.0269) in the new condition.

The graph in FIG. 7B shows the driving force F and slip ratio S when running on new tires (a different type of tire from FIG. 7A), and the same type of worn tires (W = 8 mm). 3 plots the driving force F and the slip ratio S for each case. As in the case of FIG. 7A, when the regression coefficient is calculated for each data set of the new tire state and the worn state, the slope f1 in the worn state is 0.0191, and the slope f1 _N (=0.0534) in the new state. became smaller.

By the way, it is known that the shear stiffness k _x per unit area is affected by the ambient temperature. More specifically, the shear stiffness k _x per unit area decreases as the temperature increases, and increases as the temperature decreases. Therefore, even if the condition of the road surface on which the tire travels and the amount of wear of the tire are the same, the slope f1 increases as the temperature rises, and decreases as the temperature decreases.

In order to prove this, the inventor conducted an experiment to measure the temperature dependence of the slope f1 for various types of tires TY1 to TY12. The experiment was carried out by mounting tires on the vehicle, running the vehicle, and calculating the slope f1 from the output value of the sensor mounted on the vehicle, as in the experiment of FIGS. 7A and 7B. The results of the experiments are shown graphically in Figures 8A-8D. The horizontal axis of each graph is the temperature T (° C.) of the vehicle, and the vertical axis is the calculated slope f1. In FIGS. 8A-8D, for the same type of tire, the left side shows a new state graph, and the right side shows a completely worn state graph. The term "completely worn state" as used herein means a state in which a slip sign appears and the groove depth is 1.6 mm. As can be seen from FIGS. 8A to 8D, in all tires, the lower the temperature T, the smaller the slope f1, and the higher the temperature T, the larger the slope f1. From this, it can be seen that the temperature dependence of the slope f1 can be well expressed by linear regression of the temperature T and the slope f1 data set.

As described above, for the control using the gradient f1 of the driving force F with respect to the slip ratio S, such as estimation of the tire wear state and judgment of the road surface condition, the influence of the temperature T is reduced in order to improve the calculation accuracy of the gradient f1. Consideration is required.

Referring to FIG. 3 again, in step S13, the tilt correction unit 30 corrects the tilt f1 calculated in step S12 to cancel the influence of the temperature T. FIG. In this embodiment, the reference temperature is T1 (° C.), and the slope f1 is corrected based on the following equation.
f1 = f1 - a ₃ × (T - T1)

The coefficient _a3 is an index representing the extent to which the slope f1 depends on the temperature T, and in this embodiment, indicates the extent to which the slope f1 changes with respect to the difference between the temperature T at the time of correction and the predetermined reference temperature T1. is a positive constant. The coefficient a ₃ can be specified by performing regression analysis on a large number of data sets of the temperature T and the slope f1 if the reference temperature T1 is determined. The coefficient a ₃ may be specified for each type of tire and stored in the ROM 13 or storage device 15. The tilt correction unit 30 acquires information on the type of tire mounted on the vehicle 1, may be configured to read a coefficient a ₃ suitable for , from the ROM 13 or the storage device 15 to correct the slope f1. Alternatively, a representative coefficient a ₃ may be determined and stored in the ROM 13 or storage device 15 regardless of the type of tire.

Even if the reference temperature T1 is not particularly determined, by performing regression analysis on a large number of data sets of the temperature T and the slope f1, the slope a ₄ and the intercept b ₄ of the regression line shown below can be obtained in advance. It may be determined in advance and used for tilt correction by the tilt correction unit 30 .
f1= _a4 ×T+ _b4

If the slope f1 calculated in step S12 and corrected in step S13 is not derived from a data set acquired while driving on dry asphalt, the slope f1 is not used for estimating the state of wear and the process proceeds to step S1. back to If the slope f1 calculated in step S12 is derived from a data set obtained while driving on dry asphalt, the estimator 31 compares the slope f1 with a predetermined threshold. The predetermined threshold is specified in advance by experiment or simulation and stored in the ROM 13 or storage device 15 . When the slope f1 exceeds a predetermined threshold value, the estimating unit 31 estimates that the groove depth of the tire is deeper than the reference value for determining wear and that the tire is not worn. After that, the process returns to step S1.

On the other hand, when the slope f1 is equal to or less than the predetermined threshold value, the estimating unit 31 estimates that the depth of the groove of the tire is shallower than the reference value for determining that the tire is worn, and that the tire is in a worn state. In the subsequent step S14, the estimating section 31 generates a signal for notifying wear of the tire, and causes the display 3 to display the notification to the driver. The content of the notification displayed on the display 3 may include, for example, that the tire is worn to a reference value or more, that the tire is likely to slip, and that the tire should be replaced. The mode of notification is not particularly limited, and can be appropriately selected from a text message, icon lighting, graphic display, and the like. Also, a notification including similar content may be output by voice through the speaker of the vehicle 1 .

<2. Second Embodiment>
A device, method, and program according to the second embodiment of the present invention will be described below. The device according to the second embodiment is configured as a device (determination device) that determines the state of the road surface on which the vehicle 1 travels. Since the gradient f1 of the driving force F with respect to the slip ratio S also changes depending on the road surface condition, the condition of the road surface on which the vehicle 1 travels can be determined by monitoring the gradient f1 in a shorter period than the estimation of the wear condition. It is possible to As described above, the slope f1 also depends on the external temperature of the vehicle 1 . Therefore, as in the first embodiment, it is important to cancel the influence of the temperature from the slope f1 in order to improve the accuracy of determining the road surface condition. In the following, the configuration and processing procedures (steps) that are different from those of the first embodiment will be mainly described, and the configurations and steps that are common to those of the first embodiment will be given the same reference numerals, and their description will be omitted.

<2-1. Configuration of Device for Determining Road Condition>
FIG. 1 is a schematic diagram showing a state in which a control unit 2A as a determination device is mounted on a vehicle 1. The vehicle 1, a display device 3, a lateral acceleration sensor 4, a wheel speed sensor 6, a torque sensor 7, a yaw rate sensor. 8 and the temperature sensor 9 are the same as in the first embodiment.

FIG. 9 is a block diagram showing the electrical configuration of the control unit 2A. Most of the electrical configuration of the control unit 2A is common to the electrical configuration of the control unit 2, but the program 10A for controlling the operation of each part of the vehicle 1 stored in the ROM 13 is different from the program 10. . As a result, the CPU 12 reads out the program 10A from the ROM 13 and executes it to virtually obtain the rotation speed acquisition unit 21, the driving force acquisition unit 22, the lateral acceleration acquisition unit 23, the turning radius acquisition unit 24, and the temperature acquisition unit 25. , the slip ratio calculation unit 26, the relationship identification unit 27, the correction unit 28, the inclination calculation unit 29, the inclination correction unit 30, and the determination unit 31A. The operation of each section 21 to 30 is common to that of the control unit 2 . The operation of the determination section 31A will be described later.

<2-2. Estimation Process of Road Condition>
FIG. 10 is a flow chart showing the flow of determination processing for determining the state of the road surface by the control unit 2A. This determination process may be repeatedly executed while the electric system of the vehicle 1 is powered on.

As can be seen from FIG. 10, the determination processing by the control unit 2A is common to the wear state estimation processing by the control unit 2 up to the step until the tilt correction section 30 corrects the tilt f1 calculated in step S12. That is, steps S1 to S13 in FIG. 10 are the same as steps S1 to S13 of the estimation process according to the first embodiment already described, so the processes after step S13 will be described below.

In the determination process by the control unit 2A, after step S13, the process proceeds to step S15. In step S15, the determination unit 31A compares the corrected slope f1 with a predetermined threshold value for road surface determination. The predetermined threshold value may be a value determined in advance by experiment or simulation and stored in the ROM 13 or storage device 15 . The determining unit 31A determines that the road surface is not slippery if the slope f1 is less than a predetermined threshold. After that, the process returns to step S1. On the other hand, if the slope f1 is equal to or greater than the predetermined threshold value, the determination unit 31A determines that hydroplaning or the like is likely to occur and that the road surface is in a slippery state. If the determination unit 31A determines that the road surface is in a slippery state, the process proceeds to step S16.

In step S16, the determination unit 31A generates a signal that warns that the road surface is slippery, and causes the display 3 to display the warning to the driver. The mode of notification is not particularly limited, and can be appropriately selected from a text message, icon lighting, graphic display, and the like. Also, a notification including similar content may be output by voice through the speaker of the vehicle 1 . Further, the determination unit 31A calculates an index indicating slipperiness according to the slope f1, and transfers this to various control processes executed on the control unit 2A. Examples of the control referred to here include brake control when the vehicle is running, control of the inter-vehicle distance, and the like.

<3. Variation>
Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the invention. For example, the following changes are possible. Also, the gist of the following modified examples can be combined as appropriate.

<3-1>
The tire wear state estimation and road surface state determination according to the above embodiment can be applied to a rear-wheel drive vehicle, and can also be applied to a four-wheel drive vehicle. Furthermore, the same function is not limited to four-wheeled vehicles, and can be applied to three-wheeled vehicles or six-wheeled vehicles as appropriate. When the tire wear condition estimation according to the above embodiment is applied to a rear-wheel drive vehicle, the average wear amount of the tires mounted on the rear wheels, which are driving wheels, is estimated.

<3-2>
The method of obtaining the lateral acceleration γ of the vehicle 1 is not limited to that described in the above embodiment. For example, the lateral acceleration γ can also be obtained from information on the yaw rate ω and the rotation speeds V1 to V4 from the yaw rate sensor 8.

<3-3>
In the above embodiment, the method of calculating the vehicle body speed used to calculate the slip ratio S, turning radius R, etc. is not limited to that described in the above embodiment. For example, the slip ratio S, the turning radius R, and the like may be calculated using the vehicle body speed as a value obtained by integrating the acceleration α acquired by the acceleration sensor attached to the vehicle 1 . Alternatively, the vehicle speed may be calculated from the positioning signal of a satellite positioning system such as GPS connected to the vehicle 1, and used to calculate the slip ratio S, the turning radius R, and the like.

<3-4>
The method of obtaining the driving force F is not limited to that described in the above embodiment. For example, the driving force F can be derived from the output value of an acceleration sensor attached to the vehicle 1, or it can be derived from the engine torque and the engine speed obtained from the engine control device of the vehicle 1. Alternatively, it can be derived from the tire rotation speeds V1 to V4.

<3-5>
As a method of canceling the influence of the load shift occurring during turning of the vehicle from the slip ratio S, the slip ratio S is corrected based on the relational information a ₂ , b ₂ and c ₂ , the lateral acceleration γ, and the driving force F. Alternatively, a method of calculating the slip ratio S based on any one of the following equations (3) to (5) according to the lateral acceleration γ may be used. Formula (3) is a formula for calculating the slip ratio S based only on the rotation speed of the left tire, and Formula (4) is a formula for calculating the slip ratio S based only on the rotation speed of the right tire. Formula (5) is a formula for calculating the slip ratio S based on the average rotational speed of the left and right tires.
S=(V1-V3)/V3 (3)
S=(V2-V4)/V4 (4)
S={(V1+V2)-(V3+V4)}/(V3+V4) (5)
Hereinafter, for convenience of explanation, the slip ratio S calculated by Equation (3) is the first slip ratio S, the slip ratio S calculated by Equation (4) is the second slip ratio S, and the slip ratio S calculated by Equation (5) is The slip ratio S is called a third slip ratio S.

The slip ratio calculator 26 selects one of the formulas (3) to (5) according to the latest lateral acceleration γ acquired by the lateral acceleration acquirer 23, and calculates the first slip ratio based on the selected formula. to the third slip ratio S can be calculated. More specifically, the slip ratio calculator 26 calculates the first slip ratio S when the vehicle 1 turns to the right, the second slip ratio S when the vehicle 1 turns to the left, and the third slip ratio S when the vehicle 1 runs straight. can be calculated respectively. At this time, for example, it can be determined that the vehicle is traveling straight when -A≤γ≤A, when turning right when γ<-A, and when turning left when A<γ. A is a predetermined positive threshold value.

FIG. 11 shows that when traveling straight, when turning left with a smaller lateral acceleration γ, when turning left with a larger lateral acceleration γ, when turning right with a smaller lateral acceleration γ, 3 is a graph showing linear relationships between three types of slip ratios S and driving forces F when turning to the right with a larger lateral acceleration γ. 12A to 12C are graphs plotting the relationship between the slip ratio S and the driving force F based on the measurement data when the actual vehicle is run, where the vertical axis is the slip ratio and the horizontal axis is the driving force. force F. 12A shows the relationship between the first slip ratio, the second slip ratio, and the driving force F when going straight, and FIG. 12B shows the relationship between the first slip ratio, the second slip ratio, and the driving force F when turning left. 12C shows the relationship between the first slip ratio, the second slip ratio, and the driving force F during right turning. In both graphs, the value of the slope f1 of the slip ratio S with respect to the driving force F is shown in the upper right. In FIGS. 12A to 12C, graphs are drawn for each vehicle body speed of the vehicle 1. FIG. Since the magnitude of the lateral acceleration γ is proportional to the square of the vehicle speed, the greater the vehicle speed, that is, the lower the graph in each figure, the greater the magnitude of the lateral acceleration γ.

During the turn of the vehicle 1, the centrifugal force relatively decreases the load on the inner side of the turn, and the tire slip relatively increases. Reduces tire slip. Accompanying this phenomenon, as shown in FIGS. 11 and 12A to 12C, the slope f1 of the slip ratio S with respect to the driving force F of the vehicle 1 has a large lateral acceleration γ on the inner side of the turn. It can be seen that the value converges on the outer side of the turn and becomes generally constant, although the value increases as the degree increases. Therefore, when turning left, the second slip ratio S based on the rotational speed of the right tire causes the slope f1 to converge to the smallest value. The slip ratio S causes the slope f1 to converge to the smallest value. There is no significant difference in slope f1 during straight running regardless of the slip ratio S. Therefore, either the first slip ratio or the second slip ratio may be selected instead of the third slip ratio as the slip ratio during straight running.

<3-6>
The first to third slip ratios S calculated according to the lateral acceleration γ by the above-described method are further corrected by the slip ratio S correction processing executed in step S10 of the estimation processing and determination processing according to the above embodiment. may be corrected. That is, the first to third slip ratios S calculated according to the lateral acceleration γ by the method described above may be used to calculate the slope f1, and the first to third slip ratios S are further used as the turning radius R. may be used to calculate the slope f1.

<3-7>
At least one of the correction of the slip ratio S based on the turning radius R and the correction of the slip ratio S based on the lateral acceleration γ and the driving force F may be omitted in the estimation processing and determination processing according to the above embodiment. That is, at least one of steps S8 and S10 and steps S9 and S11 may be omitted. If the slip ratio S is not corrected for the effect of turning, the data set during turning of the vehicle 1 may be selected and not used in the estimation process and determination process. Also, the order in which steps S1 to S7 are executed is not limited to the order in the above embodiment, and may be changed as appropriate.

<3-8>
In the above-described embodiment, the relational information is specified while the vehicle is running, but the relational information may be derived in advance and referred to when the slip ratio S is corrected. Also, the coefficient a ₃ for correcting the slope f1 may be specified while the vehicle 1 is running based on multiple data sets of the temperature T and the slope f1 acquired while the vehicle 1 is running.

<3-9>
In the estimation process according to the above-described embodiment, instead of the threshold value of the slope f1 for determining the wear state, the coefficient specifying the regression equation between the wear amount W (or the remaining depth of the groove) and the slope f1 is stored in the ROM 13 or stored. It may be stored in device 15 . The regression equation may be, for example, a linear equation. The coefficient specifying the regression equation can be calculated in advance by experiments or simulations based on a large number of data sets of the wear amount W (or remaining depth of the groove) and the slope f1. The estimation unit 31 may estimate the wear amount W (or the remaining depth of the groove) from the slope f1 based on the regression equation stored in the ROM 13 or storage device 15 .

<4. Evaluation>
From the data sets of the temperature T and the slope f1 (before temperature correction) plotted in the graphs of FIGS. 8A to 8D, the coefficient a ₃ for correcting the slope f1 with the temperature T was calculated for each graph. Among the calculated coefficients a3, the _average value of the maximum value and the minimum value was determined as a representative coefficient _a3 . When the slope f1 is corrected using this coefficient _a3 and the reference temperature T1, and when the slope f1 is not corrected, the slope f1 changes for different types of tires TY13 to TY17. Although not limited to this, the reference temperature T1 is set to 20° C. here. Graphs of the results are shown in FIGS. 13A and 13B. The horizontal axis of each graph is the remaining groove, and the vertical axis is the slope f1.

As shown in FIGS. 13A and 13B, in the tires TY13 to TY17, the correlation coefficient R ² is larger when the temperature correction is performed than when the temperature correction is not performed, and the remaining depth of the groove of the tire and the slope f1 become stronger. As a result, it was found that the slope f1 with respect to the slip ratio S corrected for the influence of temperature more accurately reflects the ease of slipping between the road surface and the tire. It is expected that the accuracy of road surface condition determination and the accuracy of wear condition estimation will be further improved by utilizing the gradient f1 resulting from this temperature correction in the control of determining the condition of the road surface and estimating the condition of wear.

1 vehicle 2 control unit (estimation device)
2A control unit (judgment device)
3 indicator 4 lateral acceleration sensor 6 wheel speed sensor 7 acceleration sensor 8 yaw rate sensor 9 temperature sensor 10 program 10A program 21 rotational speed acquisition unit 22 driving force acquisition unit 23 lateral acceleration acquisition unit 24 turning radius acquisition unit 25 temperature acquisition unit 26 slip ratio calculation unit 27 relationship identification unit 28 correction unit (first correction unit, second correction unit)
29 Inclination calculation unit 30 Inclination correction unit 31 Estimation unit 31A Determination unit FL Front left wheel FR Front right wheel RL Rear left wheel RR Rear right wheel V1 to V4 Tire rotation speed

Claims (13)

A device for estimating the wear state of a tire mounted on a vehicle,
a rotational speed acquisition unit that sequentially acquires rotational speeds of tires mounted on the vehicle;
a driving force acquisition unit that sequentially acquires the driving force of the vehicle;
a temperature acquisition unit that acquires the temperature outside the vehicle;
a slip ratio calculation unit that calculates a slip ratio based on the rotational speed of the tire that is sequentially acquired;
a slope calculation unit that calculates the slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force, based on a large number of data sets of the slip ratio and the driving force;
a tilt correction unit that corrects the calculated tilt based on an index representing the temperature dependence of the tilt and the temperature at the time of correction;
an estimating unit that estimates the wear state of the tire based on the corrected tilt;
Device. A device for determining the condition of a road surface on which a vehicle travels,
a rotational speed acquisition unit that sequentially acquires rotational speeds of tires mounted on the vehicle;
a driving force acquisition unit that sequentially acquires the driving force of the vehicle;
a temperature acquisition unit that acquires the temperature outside the vehicle;
a slip ratio calculation unit that calculates a slip ratio based on the rotational speed of the tire that is sequentially acquired;
a slope calculation unit that calculates the slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force, based on a large number of data sets of the slip ratio and the driving force;
a tilt correction unit that corrects the calculated tilt based on an index representing the temperature dependence of the tilt and the temperature at the time of correction;
a determination unit that determines the state of the road surface based on the corrected inclination;
Device. The index is a slope representing a linear relationship between the temperature and the slope.
3. Apparatus according to claim 1 or 2. further comprising a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle;
The slip ratio calculator calculates the slip ratio of the tire based on the rotational speed of the left tire among the rotational speeds of the tires that are sequentially obtained according to the lateral acceleration that is sequentially obtained. A first slip ratio, a second slip ratio that is the slip ratio of the tire calculated based on the rotational speed of the right tire, and a slip ratio of the tire that is calculated based on the average rotational speed of the left and right tires. sequentially selecting and acquiring any one from a group including a third slip ratio;
4. Apparatus according to any of claims 1-3. The slip ratio calculator calculates the first slip ratio when the vehicle is turning to the right, the second slip ratio when the vehicle is turning to the left, and the third slip ratio when the vehicle is traveling straight, depending on the lateral acceleration. select the slip ratio,
5. Apparatus according to claim 4. a turning radius acquisition unit that acquires a turning radius of the vehicle;
a first correction unit that corrects the slip ratio based on first relational information representing the relationship between the turning radius and the slip ratio, and the turning radius at the time of correction;
6. Apparatus according to any of claims 1-5. The first relational information is information representing the slip ratio as a quadratic function of the reciprocal of the turning radius.
7. Apparatus according to claim 6. a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle;
second relational information representing the relationship between the lateral acceleration, the driving force, and the slip ratio; and a second correction unit that corrects the slip ratio based on the lateral acceleration and the driving force at the time of correction. prepare further,
8. Apparatus according to any of claims 1-7. The second relationship information is information that represents the slip ratio as a linear function of the driving force and represents the slope of the slip ratio with respect to the driving force as a quadratic function of the lateral acceleration.
9. Apparatus according to claim 8. A method for estimating the state of wear of a tire mounted on a vehicle, comprising:
sequentially acquiring rotational speeds of tires mounted on the vehicle;
sequentially acquiring the driving force of the vehicle;
obtaining a temperature outside the vehicle;
calculating a slip ratio based on the rotational speed of the tire that is sequentially obtained;
calculating a slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force based on multiple data sets of the slip ratio and the driving force;
correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction;
estimating the wear state of the tire based on the corrected inclination;
including,
Method. A method for determining the condition of a road surface on which a vehicle travels, comprising:
sequentially acquiring rotational speeds of tires mounted on the vehicle;
sequentially acquiring the driving force of the vehicle;
obtaining a temperature outside the vehicle;
calculating a slip ratio based on the rotational speed of the tire that is sequentially obtained;
calculating a slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force based on multiple data sets of the slip ratio and the driving force;
correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction;
determining the condition of the road surface based on the corrected slope;
Method. A program for estimating the wear state of a tire mounted on a vehicle,
sequentially acquiring rotational speeds of tires mounted on the vehicle;
sequentially acquiring the driving force of the vehicle;
obtaining a temperature outside the vehicle;
calculating a slip ratio based on the rotational speed of the tire that is sequentially obtained;
calculating a slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force based on multiple data sets of the slip ratio and the driving force;
correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction;
estimating the wear state of the tire based on the corrected inclination;
cause the computer to run
program. A program for determining the condition of a road surface on which a vehicle travels,
sequentially acquiring rotational speeds of tires mounted on the vehicle;
sequentially acquiring the driving force of the vehicle;
obtaining a temperature outside the vehicle;
calculating a slip ratio based on the rotational speed of the tire that is sequentially obtained;
calculating a slope of the slip ratio with respect to the driving force as a regression coefficient representing a linear relationship between the slip ratio and the driving force based on multiple data sets of the slip ratio and the driving force;
correcting the calculated slope based on an index representing the temperature dependence of the slope and the temperature at the time of correction;
causing a computer to determine the condition of the road surface based on the corrected inclination;
program.

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