JP7543968B2 - Device for estimating tire wear condition - Google Patents

Description

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

Patent Document 1 discloses a device that can determine the condition of the road surface as well as the wear state of tires. According to the device disclosed in Patent Document 1, the slope of the relational equation between the slip ratio calculated from the wheel speed of the tire and the acceleration/deceleration of the vehicle is used as a road surface judgment value, and the judgment value is compared with a predetermined threshold value to judge the road surface condition. The threshold value is changed by a calculation formula pre-stored in the device according to the type of tire read from the tire's wireless ID tag. The tire wear state is also estimated by comparing the changed threshold value with the average judgment value when driving on asphalt.

JP 2005-138702 A

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

The present invention aims to provide an apparatus, method, and program that can accurately estimate the wear state of a tire while taking into account the effects of temperature, as well as an apparatus, method, and program that can accurately determine the condition of the road surface.

The device according to the first aspect of the present invention is a device for estimating the wear state of a tire mounted on a vehicle, and includes a rotation speed acquisition unit, a driving force acquisition unit, a temperature acquisition unit, a slip ratio calculation unit, a slope calculation unit, a slope correction unit, and an estimation unit. The rotation speed acquisition unit sequentially acquires the rotation speed of the tire mounted on the vehicle. The driving force acquisition unit sequentially acquires the driving force of the vehicle. The temperature acquisition unit acquires the temperature outside the vehicle. The slip ratio calculation unit calculates the slip ratio based on the rotation speed of the tire sequentially acquired. The slope calculation unit calculates 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. The slope correction unit corrects the calculated slope based on an index representing the temperature dependency of the slope and the temperature at the time of correction. The estimation unit estimates the wear state of the tire based on the corrected slope.

The device according to the second aspect of the present invention is a device for determining the state of a road surface on which a vehicle travels, and includes a rotation speed acquisition unit, a driving force acquisition unit, a temperature acquisition unit, a slip ratio calculation unit, a slope calculation unit, a slope correction unit, and a judgment unit. The rotation speed acquisition unit sequentially acquires the rotation speeds of tires mounted on the vehicle. The driving force acquisition unit sequentially acquires the driving force of the vehicle. The temperature acquisition unit acquires the temperature outside the vehicle. The slip ratio calculation unit calculates a slip ratio based on the rotation speeds of the tires sequentially acquired. The slope calculation unit calculates 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. The slope correction unit corrects the calculated slope based on an index representing the temperature dependency of the slope and the temperature at the time of correction. The judgment unit judges the state of the road surface based on the corrected slope.

The device according to the third aspect of the present invention is the device according to the first or second aspect, and the index is a slope that represents a linear relationship between the temperature and the slope.

The device according to a fourth aspect of the present invention is a device according to any one of the first to third aspects, further comprising a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle. The slip ratio calculation unit sequentially selects and acquires one from a group including a first slip ratio that is the slip ratio of the tire calculated based on the rotation speed of the left tire, a second slip ratio that is the slip ratio of the tire calculated based on the rotation speed of the right tire, and a third slip ratio that is the slip ratio of the tire calculated based on the average of the rotation speeds of the left and right tires, among the rotation speeds of the tires that are sequentially acquired, according to the lateral accelerations that are sequentially acquired.

The device according to the fifth aspect of the present invention is the device according to the fourth aspect, in which the slip ratio calculation unit selects the first slip ratio when the vehicle turns right, the second slip ratio when the vehicle turns left, and the third slip ratio when the vehicle travels straight, depending on the lateral acceleration.

The device according to a sixth aspect of the present invention is a device according to any one of the first to fifth aspects, further comprising a turning radius acquisition unit that acquires a turning radius of the vehicle, first relationship information that represents a relationship between the turning radius and the slip ratio, and a first correction unit that corrects the slip ratio based on the turning radius at the time of correction.

The device according to the seventh aspect of the present invention is the device according to the sixth aspect, in which the first relationship information is information that expresses the slip ratio as a quadratic function of the reciprocal of the turning radius.

The device according to the eighth aspect of the present invention is a device according to any one of the first to seventh aspects, further comprising a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle, second relationship information that represents 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.

The device according to the ninth aspect of the present invention is the device according to the eighth aspect, in which the second relationship information is information that expresses the slip ratio as a linear function of the driving force and expresses the slope of the slip ratio with respect to the driving force as a quadratic function of the lateral acceleration.

A method according to a tenth aspect of the present invention is a method for estimating a wear state 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 a wear state of a tire mounted on a vehicle, and causes a computer to execute the following.
- Sequentially acquiring the rotational speeds of the tires mounted on the vehicle.
- Sequentially acquiring the driving force of the vehicle.
- Obtaining the temperature outside the vehicle.
Calculating a slip ratio based on the rotational speeds of the tires that are successively acquired.
Calculating a 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 inclination based on an index representing the temperature dependency of the inclination and the temperature at the time of correction.
- Estimating the wear state of the tire based on the corrected slope.

A method according to an eleventh aspect of the present invention is a method for determining the condition 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 condition of a road surface on which a vehicle travels, and causes a computer to execute the following.
- Sequentially acquiring the rotational speeds of the tires mounted on the vehicle.
- Sequentially acquiring the driving force of the vehicle.
- Obtaining the temperature outside the vehicle.
Calculating a slip ratio based on the rotational speeds of the tires that are successively acquired.
Calculating a 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 inclination based on an index representing the temperature dependency of the inclination and the temperature at the time of correction.
- Determining the condition of the road surface based on the corrected inclination.

The value based on the slope of the relational equation between the slip ratio and the driving force (acceleration/deceleration) of the vehicle is used as an index for judging whether the tire is slippery 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 runs and the degree of tire wear. Since the driving stiffness is also affected by temperature, the slope of the relational equation between the slip ratio and the driving force (acceleration/deceleration) of the vehicle also changes depending on temperature. According to the first aspect of the present invention, a value based on the slope corrected for the effect of temperature is used to estimate the tire wear state. This makes it possible to estimate the tire wear state more accurately. According to the second aspect of the present invention, a value based on the slope corrected for the effect of temperature is used to judge the road surface state. This makes it possible to judge the road surface state on which the vehicle runs more accurately.

1 is a schematic diagram showing a state in which a control unit serving as an estimation device according to a first embodiment is mounted on a vehicle; FIG. 2 is a block diagram showing the electrical configuration of a control unit according to the first embodiment. 5 is a flowchart showing the flow of a wear state estimation process according to the first embodiment. 4 is 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. 5 is a graph plotting braking force coefficient and slip ratio obtained by an experiment. 5 is a graph plotting braking force coefficient and slip ratio obtained by an experiment. 6 is a graph plotting driving force and slip ratio obtained by an experiment. 6 is a graph plotting driving force and slip ratio obtained by an experiment. 1 is a graph showing the temperature dependence of the slope. 1 is a graph showing the temperature dependence of the slope. 1 is a graph showing the temperature dependence of the slope. 1 is a graph showing the temperature dependence of the slope. FIG. 11 is a block diagram showing the electrical configuration of a control unit according to a second embodiment. 10 is a flowchart showing the flow of a process for determining a road surface condition according to a second embodiment. 5 is a graph showing the relationship between various slip ratios and driving force when traveling straight, turning left, and turning right. 5 is a graph showing the relationship between the first slip ratio and the second slip ratio and the driving force for various vehicle speeds when traveling straight. 6 is a graph showing the relationship between the first slip ratio and the second slip ratio and the driving force for various vehicle speeds when turning left; 6 is a graph showing the relationship between the first slip ratio and the second slip ratio and the driving force for various vehicle speeds when turning right. 13 is a graph comparing the strength of correlation of the slope with respect to the degree of wear without and with correction. 13 is a graph comparing the strength of correlation of the slope with respect to the degree of wear without and with correction.

The following describes devices, methods, and programs according to some embodiments of the present invention with reference to the drawings.

1. First embodiment
<1-1. Configuration of device for estimating wear state>
1 is a schematic diagram showing a state in which a control unit 2 as a device (estimation device) for estimating a tire wear state according to the first embodiment is mounted on a vehicle 1. The vehicle 1 is a four-wheel vehicle and has a left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR. Tires _TFL , TFR, TRL, and _TRR are mounted on the wheels FL, _FR , _RL , and RR, respectively. The vehicle 1 according to this embodiment is a front engine, front drive vehicle (FF vehicle), with the front tire _TFL , _TFR being the driving tire, and the rear tire _TRL , _TRR being the driven tire.

The control unit 2 determines a slip ratio S, which indicates the tendency of the tires _TFL , _TFR , _TRL , and _TRR to slip while the vehicle is running, based on information on the rotation speeds of the tires _TFL , _TFR , _TRL , and _TRR while the vehicle is running, and estimates the average wear state of the tires _TFL and _TFR , which are driving wheel tires, based on the slope of the slip ratio S with respect to the driving force F of the vehicle 1. The grooves formed in the tread portion of the tire become shallower as they wear. This makes the tire more susceptible to slipping, which in turn leads to a decrease in driving force and braking force. In order to prevent such a state from becoming serious, it is generally recommended to replace the tire when the groove depth of the tread portion becomes equal to or less than a predetermined threshold value. The control unit 2 estimates the average remaining groove depth of the tires _TFL and _TFR as the wear state of the tires _TFL and _TFR , detects the timing when tire replacement is recommended, and notifies the driver of the vehicle 1 of this.

Information on the tire wear state can be used for various purposes other than prompting the driver of vehicle 1 to change tires at the appropriate time. Information on the tire wear state can be used, for example, to monitor the slipperiness of the road surface and to control the brake system.

A wheel speed sensor 6 is attached to each of 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 sensor 6 detects the rotational speed (i.e., wheel speed) V1 to V4 of the tire attached to the wheel to which the wheel speed sensor 6 is attached. V1 to V4 are the rotational speeds of the tires T _FL , T _FR , T _RL , and T _RR , respectively. Any type of wheel speed sensor 6 can be used as long as it can detect the wheel speeds of the wheels FL, FR, RL, and RR while the vehicle is moving. For example, a type of sensor that measures the wheel speed from an output signal of an electromagnetic pickup can be used, or a type of sensor that generates electricity using rotation like a dynamo and measures the wheel speed from the voltage generated at that time can be used. The attachment position of the wheel speed sensor 6 is not particularly limited, and can be appropriately selected according to the type of sensor as long as it is possible to detect the wheel speed. The wheel speed sensor 6 is connected to the control unit 2 via a communication line 5. Information on the rotation 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 is attached to the vehicle 1 to detect the wheel torque WT of the vehicle 1. The structure and mounting position of the torque sensor 7 are not particularly limited as long as it can detect the wheel torque WT of the vehicle 1. The torque sensor 7 is connected to the control unit 2 via a communication line 5. Information on the wheel torque WT detected by the torque sensor 7 is transmitted to the control unit 2 in real time, similar to the information on the rotational speeds V1 to V4.

The vehicle 1 is also fitted with a lateral acceleration sensor 4 that detects the lateral acceleration γ applied to the vehicle 1. The lateral acceleration γ is the centrifugal acceleration that acts on the vehicle 1 towards the outside of the turn when the vehicle 1 turns. The structure and mounting position of the lateral acceleration sensor 4 are not particularly limited as long as it can detect the lateral acceleration γ. The 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 transmitted to the control unit 2 in real time, similar to information on the rotational speeds V1 to V4 and the acceleration α.

The vehicle 1 is also fitted with a yaw rate sensor 8 that detects the yaw rate ω of the vehicle 1. The yaw rate ω is the rotational angular velocity around the vertical axis when the vehicle 1 turns. The yaw rate sensor 8 may be, for example, a type of sensor that detects the yaw rate using Coriolis force, but there are no particular limitations on its structure or mounting position as long as it can detect the yaw rate ω. The 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 transmitted to the control unit 2 in real time, similar to information on the rotational speeds V1 to V4, the acceleration α and the lateral acceleration γ.

The vehicle 1 is also fitted with a temperature sensor 9 that detects the temperature outside the vehicle 1. Any type of temperature sensor can be used as the temperature sensor 9 as long as it can detect the temperature outside the vehicle 1, and examples of such sensors include those that use a thermistor, a semiconductor, or a thermocouple. The location where the temperature sensor 9 is attached is not particularly limited, but it is preferable that it is attached in a location that is unlikely to be affected by the heat of the engine or exhaust of the vehicle 1. The 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 transmitted to the control unit 2 in real time, as are information on the rotational speeds V1 to V4, the wheel torque WT, the lateral acceleration γ, and the yaw rate ω.

2 is a block diagram showing the electrical configuration of the control unit 2. The control unit 2 is a computer mounted on the vehicle 1, and as shown in FIG. 2, includes an I/O interface 11, a CPU 12, a ROM 13, a RAM 14, and a non-volatile rewritable storage device 15. 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. The ROM 13 stores a program 10 for controlling the operation of each part of the vehicle 1. The CPU 12 reads out and executes the program 10 from the ROM 13, thereby virtually operating as a rotation speed acquisition unit 21, a driving force acquisition unit 22, a lateral acceleration acquisition unit 23, a turning radius acquisition unit 24, a temperature acquisition unit 25, a slip ratio calculation unit 26, a relationship identification unit 27, a correction unit 28, a tilt calculation unit 29, a tilt correction unit 30, and an estimation unit 31. Correction unit 28 is an example of the first correction unit and second correction unit of the present invention. Details of the operation of each unit 21 to 31 will be described later. Storage device 15 is composed of a hard disk, flash memory, etc. The program 10 may be stored in storage device 15 instead of ROM 13. RAM 14 and storage device 15 are used as appropriate for the calculations of CPU 12.

The display 3 can output various information, including warnings, to the user (mainly the driver), and can be realized in any form, for example, a liquid crystal display element, a liquid crystal monitor, a plasma display, an organic EL display, etc. The mounting position of the display 3 can be selected appropriately, but it is preferable to provide it in a position that is easy for the driver to see, for example, on the instrument panel. When the control unit 2 is connected to a car navigation system, it is also possible to use a monitor for the car navigation as the display 3. When a monitor is used as the display 3, the warning can be an icon or text information displayed on the monitor.

<1-2. Estimation of wear state>
Hereinafter, 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 with reference to Fig. 3. This estimation process may be executed repeatedly while the electric system of the vehicle 1 is powered on, or may be executed at a predetermined frequency, such as once a day, while the vehicle 1 is running.

In step S1, the rotational speed acquisition unit 21 acquires the rotational speeds V1 to V4 of the tires T _FL , T _FR , T _RL , and T _RR while the vehicle is running. The rotational speed acquisition unit 21 receives output signals from the wheel speed sensors 6 at a predetermined sampling period, and converts these into rotational speeds V1 to V4.

In step S2, 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 at a predetermined sampling period and converts it into the wheel torque WT.

Here, whether the process proceeds to step S3 may be determined depending on whether the data of the rotation speeds V1 to V4 and the wheel torque WT acquired in steps S1 and S2 is valid data. Valid data is data that can accurately estimate the wear state in subsequent processing, and invalid data is data that can have an undesirable effect on the estimation of the wear state. An example of invalid data is data acquired while the brakes of the vehicle 1 are operating. In this embodiment, when the data of the rotation speeds V1 to V4 and the wheel torque WT acquired in steps S1 and S2 is determined to be valid data, the process proceeds to step S3. On the other hand, when the data of the rotation speeds V1 to V4 and the wheel torque WT is determined to be invalid data, the data is discarded and the process returns to step S1.

In step S3, the lateral acceleration acquisition unit 23 acquires the lateral acceleration γ acting on the vehicle 1. The lateral acceleration acquisition unit 23 receives an output signal from the lateral acceleration sensor 4 at a predetermined sampling period and converts it into a lateral acceleration γ.

In step S4, the turning radius acquisition unit 24 acquires the yaw rate ω of the vehicle 1. The turning radius acquisition unit 24 receives an output signal from the yaw rate sensor 8 at 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. The vehicle body speed can be approximated by the speed of the driven wheels, so it can also be calculated as R = (V3 + V4) / 2ω, for example.

In step S5, 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 at a predetermined sampling period and converts it into a temperature T.

In step S6, the driving force obtaining 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 radius of the tires _TFL , _TFR , _TRL , and _TRR .

In step S7, the slip ratio calculation unit 26 calculates the slip ratio S based on the rotation speeds V1 to V4. In this embodiment, the slip ratio S is calculated as (speed of the driving wheels-vehicle speed)/vehicle speed, and the vehicle speed is the speed of the driven wheels. In this embodiment, the slip ratio S is defined as follows.
S={(V1+V2)-(V3+V4)}/(V3+V4)

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

The data of 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 acquired in steps S1 to S7, which are executed consecutively, are treated as data sets acquired at the same time or approximately the same time, and are stored in the RAM 14 or storage device 15. As shown in FIG. 3, steps S1 to S7 are executed repeatedly, so the above data sets are acquired sequentially. After step S7, when N1 such data sets (N1≧2) are accumulated, the process proceeds to steps S8 and S9. Steps S8 and S9 are executed only once. After steps S8 and S9 have been executed once, the process proceeds to step S10 after steps S1 to S7.

In step S8, the relationship identification unit 27 identifies first relationship information that represents 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. The first relationship information is used for the 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 running on the same road surface, the linear relationship between the slip ratio S and the driving force F changes compared to when traveling straight, so that the wear state may not be estimated correctly. This is because a trajectory difference (path difference) occurs between the left and right tires during turning, and the slip ratio S changes from when traveling straight due to the influence of this trajectory difference. Therefore, here, in order to realize various stable controls based on the slip ratio S, the influence caused by the trajectory difference between the left and right during turning is canceled from the slip ratio S.

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 an experiment conducted by the present inventor, the slip ratio S is generally expressed as 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 first relationship information that indicates such a relationship between the turning radius R and the slip ratio S.
S=a ₁ (1/R) ² +b ₁ (1/R)+c ₁

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 turning radius R stored in the RAM 14 or the storage device 15, and are calculated by a method such as the least squares method.

The apex of the parabola representing the relationship between the reciprocal of the turning radius R and the slip ratio S corresponds to the time of traveling straight, and as shown in Fig. 4, it generally overlaps with the vertical axis representing the slip ratio S. In other words, _b1 is generally 0. Therefore, here, it is also possible to specify only the coefficients _a1 and c1 as the _first relationship information according to the following formula.
S=a ₁ (1/R) ² +c ₁

In step S9, the relationship determination unit 27 determines second relationship information representing the relationship between the lateral acceleration γ, the driving force F, and the slip ratio S based on multiple data sets of the lateral acceleration γ, the slip ratio S, and the driving force F acquired in step S23. The second relationship information is also used for the subsequent correction of the slip ratio S (step S11). As described above, when the vehicle 1 is turning, the linear relationship between the slip ratio S and the driving force F changes, so that the wear state may not be estimated correctly. During turning, this linear relationship changes from when the vehicle is traveling straight, not only due to the difference in the left and right trajectories, but also due to the influence of the load movement in the left and right direction of the vehicle body. This is because the slip ratio S changes from when the vehicle is traveling straight due to the influence of such load movement. Therefore, in this case, in order to realize various stable controls based on the slip ratio S, the influence caused by the load movement in the left and right direction during turning is canceled from the slip ratio S.

Load transfer in the left and right direction during cornering depends on 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 an experiment conducted by the present inventor, the slope f1 is generally expressed as a quadratic function of the lateral acceleration γ, as shown in FIG. 4B. In step S9, the relationship specifying unit 27 specifies the coefficients a2, b2, _c2 , and _f2 of the following equation as second relationship information that indicates such a relationship between the lateral acceleration γ, the driving force _F , and the slip ratio S. Here, f2 is the intercept of the slip ratio S with respect to the driving force F.
S=f1F+f2=(a ₂ γ ² +b ₂ γ+c ₂ )F+f2

The coefficients _a2 , _b2 , _c2 and f2 are calculated based on multiple data sets of the slip ratio S, driving force F and lateral acceleration γ, for example using a method such as the least squares method. Alternatively, the range of lateral acceleration γ may be divided into arbitrary ranges, linear regression of the slip ratio S and driving force F may be performed in each range to calculate the regression coefficients f1 and f2, and then the average value of the lateral acceleration γ and the average value of the slope f1 may be calculated in each range, and the coefficients _a2 , _b2 and _c2 may be specified by Gaussian elimination based on these average values.

3, after steps S8 and S9 have been executed once to determine the first relationship information _a1 , _b1 , and _c1 between the turning radius R and the slip ratio S, and the second relationship information _a2 , _b2 , and _c2 between the lateral acceleration γ, the driving force F, and the slip ratio S, steps S10 to S13 are repeatedly executed each time steps S1 to S7 are executed once.

In step S10, the correction unit 28 corrects the slip ratio S acquired in the latest step S7 based on the first relationship information _a1 , _b1 , and _c1 that indicate the relationship between the turning radius R and the slip ratio S, and the turning radius R acquired in the latest step S4. As described above, the slip ratio S is expressed as 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 a value obtained by multiplying the reciprocal of the turning radius R at the time of correction by the coefficient _a1 , in accordance with the following equation.
S=S-a ₁ (1/R) ²
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 formula:
S=S-a ₁ (1/R) ² -b ₁ (1/R)

According to the above correction formula, as shown in Figure 4A, it is possible to calculate the slip ratio S when (1/R) is substantially 0, i.e., when traveling straight, and the effect of the trajectory difference due to left and right turns is cancelled from the slip ratio S.

In the next step S11, the correction unit 28 further corrects the slip ratio S acquired in step S10 based on the second relationship information _a2 , _b2 , and _c2 representing the relationship between the lateral acceleration γ and the slip ratio S, the lateral acceleration γ acquired in the latest step S3, and the driving force F acquired in the latest step S6. As described above, the slip ratio S is expressed as a linear function of the driving force F with a slope of f1, and the slope f1 is expressed as a quadratic function of the lateral acceleration γ. Therefore, the correction unit 28 calculates the sum of the value obtained by multiplying the squared value of the lateral acceleration γ at the time of correction by the coefficient _a2 , the value obtained by multiplying the lateral acceleration γ at the time of correction by the coefficient _b2 , and _c2 according to the following formula, calculates the product of the sum and the driving force F at the time of correction, and subtracts the product from the slip ratio S acquired in step S10 to further correct the slip ratio S.
S=S-f1F=S-(a ₂ γ ² +b ₂ γ+c ₂ )F

Since _b2 is also approximately 0, the slip ratio S may be corrected according to the following formula:
S=S-(a ₂ γ ² +c ₂ )F

The above correction formula makes it possible to calculate the slip ratio S converted when traveling straight, and the effect of the load shift in the left and right direction caused by turning left and right can be cancelled from the slip ratio S.

In step S12, the slope calculation unit 29 calculates the slope f1 and intercept f2 of the slip ratio S with respect to the driving force F as regression coefficients representing the linear relationship between the driving force F and the slip ratio S, based on multiple data sets of the driving force F and the corrected slip ratio S. The slope f1 and intercept f2 can be calculated, for example, by the least squares method. The slope f1 and intercept f2 may be calculated sequentially or by batch processing, based on multiple data sets of the driving force F and the slip ratio S. In this embodiment, the sequential least squares method is used as a preferred example.

In order to calculate a reasonable slope f1 and intercept f2, it is preferable that the data on the driving force F over a specified period have a certain level 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 traveling at a constant speed downhill, there is little variation in the data set. Therefore, at the current time when the wear state is estimated, it may be determined whether the variation in the driving force F is equal to or greater than a certain value, and if it is determined that the variation is equal to or greater than the certain value, the slope calculation unit 29 may calculate the slope f1 and intercept f2. The variation in the driving force F can be determined, for example, from the width and variance of the driving force F obtained over the most recent specified period, and if these are equal to or greater than a specified threshold, it can be determined that the variation is equal to or greater than a certain value.

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

It is generally known that when the road surface condition is constant, a relationship as shown in the graph of Fig. 5 holds between the slip ratio S and the driving force F. In the graph of Fig. 5, the horizontal axis represents the slip ratio S, and the vertical axis represents the driving force F. In an environment in which the vehicle 1 normally travels, the slip ratio S transitions generally within a range of 0 to Sc. As can be seen from Fig. 5, in the region in which the slip ratio S is 0 to Sc, it can be said that an approximate linear relationship holds between the slip ratio S and the driving force F, and the driving stiffness represented by the following formula (1) is known as one of the factors that govern this approximate linear relationship.
C=wk _x l ² /2 (1)

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

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

The inventor conducted an experiment to support the above. Figures 6 to 7 are graphs showing the results of each experiment. First, the inventor measured the braking force coefficient μ for the slip ratio S of the tire using the same type of tires 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 groove depth of the current tire from the groove depth of the tire in a new state. This measurement was performed using dedicated experimental equipment for measuring the μ-S characteristics for each tire under the condition of the same dry asphalt road surface. The results are shown in the graphs of Figures 6A and 6B. The graph of Figure 6B shows in detail the range of the slip ratio S of 0 to 0.1 in the graph of Figure 6A. As can be seen from Figures 6A and 6B, as the wear amount W increases, the braking force coefficient μ increases for the same slip ratio S. This confirmed that the shear stiffness 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 _kx per unit area, it is considered that the slope f1 becomes smaller as the amount of wear W increases.

Therefore, the inventor conducted further experiments to prove that the slope f1 becomes smaller as the wear amount W increases. Figures 7A and 7B are graphs showing the results of the experiments. The experiments were carried out by calculating the slope f1 when the vehicle was driven straight with tires in a new condition (W = 0) on all four wheels and when the vehicle was driven straight with tires in a worn condition on all four wheels. The same vehicle was used, and the road surface on which the vehicle was driven 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 described later. The graph in Figure 7A plots the driving force F and slip ratio S when the vehicle was driven with tires in a new condition, and the driving force F and slip ratio S when the vehicle was driven with tires in the same type of wear condition (W = 6 mm). When the regression coefficients were calculated for the data sets of the new and worn tires, 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 plots the driving force F and slip ratio S when running on new tires (a different type of tire from that in Fig. 7A) and when running on tires of the same type of wear (W = 8 mm). As in the case of Fig. 7A, when the regression coefficients were calculated for the data sets of the new and worn tires, the slope f1 in the worn condition was 0.0191, which was smaller than the slope _f1N (= 0.0534) in the new condition.

Incidentally, it is known that the shear stiffness _kx per unit area is affected by the ambient temperature. More specifically, the higher the temperature, the smaller the shear stiffness _kx per unit area, and the lower the temperature, the larger the shear stiffness kx. Therefore, even if the condition of the road surface on which the tire runs and the amount of tire wear are the same, it is considered that the slope f1 becomes larger when the temperature is higher and the slope f1 becomes smaller when the temperature is lower.

To support this, the inventors conducted an experiment to measure the temperature dependency of the slope f1 for various types of tires TY1 to TY12. The experiment was conducted by mounting the tires on a vehicle and running the vehicle, and calculating the slope f1 from the output value of a sensor mounted on the vehicle, as in the experiment in FIG. 7A and FIG. 7B. The results of the experiment are shown in the graphs of FIG. 8A to FIG. 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 FIG. 8A to FIG. 8D, for the same type of tire, a graph of a new tire is shown on the left, and a graph of a completely worn tire is shown on the right. The completely worn tire is a tire in which slip signs appear and the tread depth is 1.6 mm. As can be seen from FIG. 8A to FIG. 8D, for all tires, the slope f1 was small when the temperature T was low, and the slope f1 was large when the temperature T was high. This shows that the temperature dependency of the slope f1 can be well expressed by linear regression of the data set of the temperature T and the slope f1.

In view of the above, when using control that uses the slope f1 of the driving force F relative to the slip ratio S, such as estimating the state of tire wear or determining the state of the road surface, it is necessary to take into account the effect of temperature T in order to improve the calculation accuracy of the slope f1.

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

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

Incidentally, even if the reference temperature T1 is not specifically determined, a regression analysis may be performed on a large number of data sets of the temperature T and the slope f1 to determine in advance the slope _a4 and intercept _b4 of the regression line shown below, and these may be used for the slope correction by the slope correction unit 30.
f1 = _a4 x T + _b4

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

On the other hand, when the slope f1 is equal to or less than a predetermined threshold, the estimation unit 31 estimates that the tire groove depth is shallower than the reference value for judging wear, and that the tire is in a worn state. In the subsequent step S14, the estimation unit 31 generates a signal notifying the driver of tire wear, and displays a notification to the driver via the display unit 3. The content of the notification displayed on the display unit 3 may include, for example, that the tire has worn down beyond the reference value, that the tire is prone to slipping, and a recommendation to change the tire. The form of the notification is not particularly limited, and may be appropriately selected from a message using text information, the illumination of an icon, the display of a graphic, and the like. A notification including the same content may also be output as audio via the speaker of the vehicle 1.

<2. Second embodiment>
Hereinafter, a device, a method, and a program according to the second embodiment of the present invention will be described. The device according to the second embodiment is configured as a device (determination device) for determining the state of the road surface on which the vehicle 1 runs. Since the slope f1 of the driving force F with respect to the slip ratio S also changes depending on the state of the road surface, it is possible to determine the state of the road surface on which the vehicle 1 runs by monitoring the slope f1 in a short period compared to the estimation of the wear state. As described above, the slope f1 also depends on the external temperature of the vehicle 1. For this reason, as in the first embodiment, it is important to cancel the influence of temperature from the slope f1 in order to improve the accuracy of the determination of the road surface state. Below, the configuration and processing procedure (steps) different from the first embodiment will be mainly described, and the configuration and steps common to the first embodiment will be assigned the same reference numerals and will not be described.

2-1. Configuration of the device for determining road surface conditions
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, and the configurations of the vehicle 1, the display 3, the lateral acceleration sensor 4, the wheel speed sensor 6, the torque sensor 7, the yaw rate sensor 8 and the temperature sensor 9 are each common to the first embodiment.

Figure 9 is a block diagram showing the electrical configuration of control unit 2A. Most of the electrical configuration of control unit 2A is the same as that of control unit 2, but program 10A, which is stored in ROM 13 and is used to control the operation of each part of vehicle 1, is different from program 10. As a result, by reading and executing program 10A from ROM 13, CPU 12 virtually operates as rotational speed acquisition unit 21, driving force acquisition unit 22, lateral acceleration acquisition unit 23, turning radius acquisition unit 24, temperature acquisition unit 25, slip ratio calculation unit 26, relationship determination unit 27, correction unit 28, tilt calculation unit 29, tilt correction unit 30, and judgment unit 31A. The operation of each of units 21 to 30 is the same as that of control unit 2. The operation of judgment unit 31A will be described later.

<2-2. Road surface condition estimation process>
10 is a flowchart showing the flow of a determination process for determining the road surface condition 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 process by the control unit 2A is the same as the wear condition estimation process by the control unit 2 up to the step where the slope correction unit 30 corrects the slope f1 calculated in step S12. In other words, 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 process from step S13 onwards will be described below.

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

In step S16, the determination unit 31A generates a signal to warn that the road surface is slippery, and displays the warning to the driver via the display 3. The form of the notification is not particularly limited, and can be appropriately selected from a text message, an icon light, a graphic display, and the like. A notification containing similar content may also be output as audio via the speaker of the vehicle 1. Furthermore, the determination unit 31A calculates an index indicating the slipperiness according to the inclination f1, and passes this to various control processes executed on the control unit 2A. Examples of the control referred to here include brake control and vehicle distance control while the vehicle is traveling.

3. Modifications
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the following modifications are possible. In addition, the gist of the following modifications 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 rear-wheel drive vehicles and four-wheel drive vehicles. Furthermore, the same function is not limited to four-wheel vehicles, but can also be appropriately applied to three-wheel vehicles or six-wheel vehicles. When the tire wear state estimation according to the above embodiment is applied to a rear-wheel drive vehicle, the average amount of wear of the tires mounted on the rear wheels, which are the driving wheels, is estimated.

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

<3-3>
In the above embodiment, the method of calculating the vehicle 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, turning radius R, etc. may be calculated by integrating the acceleration α acquired by an acceleration sensor attached to the vehicle 1 as the vehicle speed. In addition, the vehicle speed may be calculated from a positioning signal of a satellite positioning system such as GPS that is communicatively connected to the vehicle 1, and used to calculate the slip ratio S, turning radius R, etc.

<3-4>
The method of acquiring 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 from the engine torque and engine speed acquired from a control device of the engine of the vehicle 1, or from the tire rotation speeds V1 to V4.

<3-5>
As a method for canceling the effect of load transfer occurring during turning of the vehicle from the slip ratio S, instead of correcting the slip ratio S based on the relationship information _a2 , _b2 , and _c2 , the lateral acceleration γ, and the driving force F, it is also possible to use a method of calculating the slip ratio S based on any of the following equations (3) to (5) according to the lateral acceleration γ. Equation (3) is an equation for calculating the slip ratio S based only on the rotational speed of the left tire, equation (4) is an equation for calculating the slip ratio S based only on the rotational speed of the right tire, and equation (5) is an equation for calculating the slip ratio S based on the average of the rotational speeds 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 ease of explanation, the slip ratio S calculated using equation (3) will be referred to as the first slip ratio S, the slip ratio S calculated using equation (4) will be referred to as the second slip ratio S, and the slip ratio S calculated using equation (5) will be referred to as the third slip ratio S.

The slip ratio calculation unit 26 can select one of the formulas (3) to (5) according to the latest lateral acceleration γ acquired by the lateral acceleration acquisition unit 23, and calculate one of the first to third slip ratios S based on the selected formula. More specifically, the slip ratio calculation unit 26 can calculate the first slip ratio S when the vehicle 1 turns right, the second slip ratio S when the vehicle 1 turns left, and the third slip ratio S when the vehicle 1 travels straight. At this time, it can be determined that the vehicle is traveling straight when -A≦γ≦A, that the vehicle is turning right when γ<-A, and that the vehicle is turning left when A<γ. A is a threshold value that takes a predetermined positive value.

Figure 11 is a graph showing the linear relationship between three types of slip ratios S and driving force F when going straight, when turning left with a smaller magnitude of lateral acceleration γ, when turning left with a larger magnitude of lateral acceleration γ, when turning right with a smaller magnitude of lateral acceleration γ, and when turning right with a larger magnitude of lateral acceleration γ. Also, Figures 12A to 12C are graphs plotting the relationship between slip ratio S and driving force F based on measurement data when an actual vehicle is driven, with the vertical axis representing slip ratio and the horizontal axis representing driving force F. Figure 12A shows the relationship between the first and second slip ratios and driving force F when going straight, Figure 12B shows the relationship between the first and second slip ratios and driving force F when turning left, and Figure 12C shows the relationship between the first and second slip ratios and driving force F when turning right. In each graph, the value of the slope f1 of the slip ratio S with respect to the driving force F is shown in the upper right corner. In Figures 12A to 12C, a graph is drawn for each vehicle speed of the vehicle 1. Note that since the magnitude of the lateral acceleration γ is proportional to the square of the vehicle speed, the magnitude of the lateral acceleration γ increases as the vehicle speed increases, i.e., the graphs are lower in each figure.

During the turning of the vehicle 1, on the inside of the turn, the load is relatively reduced due to centrifugal force, and the tire slip is relatively increased, while on the outside of the turn, the load is relatively increased, and the tire slip is relatively decreased. In addition, as shown in Figures 11 and 12A to 12C, the slope f1 of the slip ratio S with respect to the driving force F of the vehicle 1 increases as the magnitude of the lateral acceleration γ increases on the inside of the turn, but on the outside of the turn, the value converges and becomes roughly constant. Therefore, when turning left, the second slip ratio S based on the rotational speed of the right tire converges the slope f1 to the smallest value, and when turning right, the first slip ratio S based on the rotational speed of the left tire converges the slope f1 to the smallest value. When traveling straight, there is no significant difference in the slope f1 regardless of the slip ratio S. For this reason, the slip ratio when traveling straight may be selected to be either the first slip ratio or the second slip ratio, rather than the third slip ratio.

<3-6>
The first to third slip ratios S calculated according to the lateral acceleration γ by the above-mentioned method may be further corrected by a correction process for the slip ratio S executed in step S10 of the estimation process and determination process according to the above-mentioned embodiment. In other words, the first to third slip ratios S calculated according to the lateral acceleration γ by the above-mentioned method may be used to calculate the slope f1, or the first to third slip ratios S may be further corrected based on relationship information with the turning radius R and used to calculate the slope f1.

<3-7>
In the estimation process and the determination process according to the above embodiment, 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. That is, at least one of steps S8 and S10 and steps S9 and S11 may be omitted. When the slip ratio S is not corrected for the effect of turning, a data set when the vehicle 1 is turning may be selected so as not to be used in the estimation process and the determination process. Furthermore, the order of executing steps S1 to S7 is not limited to that of the above embodiment and may be changed as appropriate.

<3-8>
In the above embodiment, the relationship information is identified while the vehicle is running, but the relationship information may be derived in advance and referred to when correcting the slip ratio S. Furthermore, the coefficient _a3 for correcting the slope f1 may be identified while the vehicle 1 is running, based on a large number of 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 embodiment, instead of a threshold value of the slope f1 for determining the wear state, a coefficient specifying a regression equation between the wear amount W (or the remaining groove depth) and the slope f1 may be stored in the ROM 13 or the storage device 15. The regression equation may be, for example, a linear equation. The coefficient specifying the regression equation may be calculated in advance by experiment or simulation based on a large number of data sets of the wear amount W (or the remaining groove depth) and the slope f1. The estimation unit 31 may estimate the wear amount W (or the remaining groove depth) from the slope f1 based on the regression equation stored in the ROM 13 or the storage device 15.

4. Evaluation
From the data set of temperature T and slope f1 (before temperature correction) plotted on the graphs of Figures 8A to 8D, a coefficient _a3 for correcting the slope f1 with temperature T for each graph was calculated. The average value of the maximum and minimum values of the calculated coefficients _a3 was determined as a representative coefficient _a3 . The change in slope f1 with respect to the remaining depth (remaining groove) of the tire groove measured when the slope f1 was corrected using this coefficient _a3 and the reference temperature T1 was compared for each of different types of tires TY13 to TY17. Note that, although not limited thereto, the reference temperature T1 was set to 20°C here. The graphs of the results are shown in Figures 13A and 13B. The horizontal axis of each graph is the remaining groove, and the vertical axis is the slope f1.

13A and 13B, for tires TY13 to TY17, the correlation coefficient ^R2 was larger when temperature correction was performed than when temperature correction was not performed, and the linear relationship between the remaining tire groove depth and the slope f1 was stronger. This shows that the slope f1 for the slip ratio S corrected for the effect of temperature more accurately reflects the ease of slipping between the road surface and the tire. By utilizing the slope f1 resulting from temperature correction in determining the road surface condition and controlling the estimation of the wear state, it is expected that the accuracy of determining the road surface condition and the accuracy of estimating the wear state will be further improved.

1 Vehicle 2 Control unit (estimation device)
2A Control unit (judgment device)
3 Display 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 determination 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 Left front wheel FR Right front wheel RL Left rear wheel RR Right rear wheel V1 to V4 Tire rotation speed

Claims (13)

A device for estimating a wear state of a tire mounted on a vehicle, comprising:
A rotation speed acquisition unit that sequentially acquires the rotation speeds of tires mounted on the vehicle;
a driving force acquisition unit that sequentially acquires driving forces of the vehicle;
a temperature acquisition unit that acquires a temperature outside the vehicle;
a slip ratio calculation unit that calculates a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
a gradient calculation unit that calculates a gradient of the slip ratio with respect to the driving force based on a large number of data sets of the slip ratio and the driving force as a regression coefficient that represents a linear relationship between the slip ratio and the driving force;
a slope correction unit that corrects the calculated slope based on an index representing the temperature dependency of the slope and the temperature at the time of correction;
and an estimation unit that estimates a wear state of the tire based on the corrected inclination.
Device. A device for determining a condition of a road surface on which a vehicle is traveling, comprising:
A rotation speed acquisition unit that sequentially acquires the rotation speeds of tires mounted on the vehicle;
a driving force acquisition unit that sequentially acquires driving forces of the vehicle;
a temperature acquisition unit that acquires a temperature outside the vehicle;
a slip ratio calculation unit that calculates a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
a gradient calculation unit that calculates a gradient of the slip ratio with respect to the driving force based on a large number of data sets of the slip ratio and the driving force as a regression coefficient that represents a linear relationship between the slip ratio and the driving force;
a slope correction unit that corrects the calculated slope based on an index representing the temperature dependency of the slope and the temperature at the time of correction;
and a determination unit that determines a state of the road surface based on the corrected inclination.
Device. The index is a slope that represents a linear relationship between the temperature and the slope.
3. Apparatus according to claim 1 or 2. A lateral acceleration acquisition unit is further provided for sequentially acquiring lateral acceleration applied to the vehicle,
the slip ratio calculation unit sequentially selects and acquires, in response to the sequentially acquired lateral acceleration, one from a group including a first slip ratio which is the slip ratio of the tire calculated based on the rotational speed of a left tire, a second slip ratio which is the slip ratio of the tire calculated based on the rotational speed of a right tire, and a third slip ratio which is the slip ratio of the tire calculated based on an average of the rotational speeds of the left and right tires among the sequentially acquired rotational speeds of the tires;
4. Apparatus according to any one of claims 1 to 3. the slip ratio calculation unit selects, in response to the lateral acceleration, the first slip ratio when the vehicle is turning right, the second slip ratio when the vehicle is turning left, and the third slip ratio when the vehicle is traveling straight.
5. The apparatus of 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 relationship information that indicates a relationship between the turning radius and the slip ratio and the turning radius at the time of correction,
6. Apparatus according to any one of claims 1 to 5. The first relationship information is information expressing the slip ratio as a quadratic function of the reciprocal of the turning radius.
7. The apparatus of claim 6. a lateral acceleration acquisition unit that sequentially acquires lateral acceleration applied to the vehicle;
a second correction unit that corrects the slip ratio based on second relationship information that indicates a relationship between the lateral acceleration, the driving force, and the slip ratio, and the lateral acceleration and the driving force at the time of correction,
8. Apparatus according to any one of claims 1 to 7. The second relationship information is information that expresses the slip ratio as a linear function of the driving force, and expresses a slope of the slip ratio with respect to the driving force as a quadratic function of the lateral acceleration.
9. The apparatus of claim 8. A method for estimating a wear state of a tire mounted on a vehicle, comprising the steps of:
Sequentially acquiring rotational speeds of tires mounted on the vehicle;
Sequentially acquiring driving forces of the vehicle;
obtaining a temperature outside the vehicle;
Calculating a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
Calculating a 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 temperature dependency of the slope and the temperature at the time of correction;
estimating a wear state of the tire based on the corrected slope; and
Including,
method. 1. A method for determining a condition of a road surface on which a vehicle is traveling, comprising:
Sequentially acquiring rotational speeds of tires mounted on the vehicle;
Sequentially acquiring driving forces of the vehicle;
Obtaining a temperature outside the vehicle;
Calculating a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
Calculating a 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 temperature dependency of the slope and the temperature at the time of correction;
and determining a state of the road surface based on the corrected inclination.
method. A program for estimating a wear state of a tire mounted on a vehicle, comprising:
Sequentially acquiring rotational speeds of tires mounted on the vehicle;
Sequentially acquiring driving forces of the vehicle;
Obtaining a temperature outside the vehicle;
Calculating a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
Calculating a 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 temperature dependency of the slope and the temperature at the time of correction;
estimating a wear state of the tire based on the corrected slope; and
to cause a computer to execute
program. A program for determining a condition of a road surface on which a vehicle is traveling,
Sequentially acquiring rotational speeds of tires mounted on the vehicle;
Sequentially acquiring driving forces of the vehicle;
obtaining a temperature outside the vehicle;
Calculating a slip ratio based on the rotational speeds of the tires that are sequentially acquired;
Calculating a 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 temperature dependency of the slope and the temperature at the time of correction;
and determining a condition of the road surface based on the corrected inclination.
program.