JP7781492B2 - Tire wear condition evaluation method and tire wear condition evaluation device - Google Patents

Description

The present invention relates to a tire wear condition evaluation method and a tire wear condition evaluation device.

For example, one common method for efficiently transporting finished vehicles such as automobiles mass-produced in a factory to a specified location such as a shipping point is to load multiple finished vehicles into a loading vessel such as a container, transport the loading vessel by land to a port near the destination in a transport vehicle such as a large truck, and then transfer the loading vessel to a transport vessel for water transport to the destination (see, for example, Patent Document 1).

Patent Document 2 also proposes a system in which a transport vehicle, which uses an unmanned, automatic towing vehicle to tow multiple carts along a predetermined route within a limited area, transports the completed vehicle to be transported, loaded onto the cart, to its destination.

Japanese Patent Application Laid-Open No. 2004-123258 Japanese Patent Application Laid-Open No. 2019-36036 Japanese Patent Application Publication No. 11-326145 JP 2008-143460 A

In recent years, the manufacturing industry has also seen an increasing need to take measures to compensate for labor shortages in preparation for the coming aging society. From this perspective, when considering how to transport completed vehicles efficiently with a small number of people, one possible method would be to make the transport vehicles self-propelled, as described in Patent Document 2, and then manufacture them at low cost and prepare a large number of them, so that each completed vehicle can be loaded onto the transport vehicle and transported automatically.

As mentioned above, when considering repeatedly loading completed vehicles onto a transport vehicle for automatic transport, it becomes necessary to periodically evaluate the wear state of the vehicle's contact area, specifically the tires. Patent Document 3 proposes a tire wear life prediction method that calculates the tire's friction energy during free rolling, the tire's friction energy when a toe angle is applied, the tire's friction energy when a lateral force is applied, the tire's friction energy when a driving force is applied, and the tire's friction energy when a braking force is applied, as well as the wear resistance index of the rubber in the tire tread, and predicts the tire's wear life based on the wear resistance index and each friction energy.

Patent Document 4 also proposes a method for estimating tire wear using a tire wear estimation device that includes a GPS receiver, vehicle speed detection means for detecting the vehicle speed from position data obtained by the GPS receiver, wheel rotation speed measurement means for measuring the rotation speed of the wheels, and wear estimation means for estimating the amount of tire wear from the detected vehicle speed and wheel rotation speed.

In the prediction method described in Patent Document 3, each frictional energy is measured using a specified energy measurement device. However, the frictional energy of actual tires varies greatly depending on the load conditions imposed on the tires, such as driving conditions and the weight and center of gravity of the vehicle being transported. As a result, it is impossible to accurately reproduce the complex load conditions of real-world conditions at the laboratory level, making it difficult to accurately evaluate the wear state of the tires of transport vehicles.

The method described in Patent Document 4 measures the actual vehicle speed and wheel rotation speed while traveling and estimates the amount of wear based on these measured speeds, so it appears that it can evaluate the actual state of tire wear with a higher degree of accuracy than the prediction method described in Patent Document 3. However, this method requires at least a sensor to measure the wheel rotation speed and a sensor to measure the tire internal pressure, which complicates the configuration of the transport vehicle. Furthermore, the increased number of parts that need to be installed increases manufacturing costs.

The above-mentioned problems are not limited to guided vehicles used to transport vehicles, but can also occur in guided vehicles used to transport objects other than vehicles. Furthermore, they can occur in all types of autonomous vehicles.

In light of the above, the technical problem to be solved in this specification is to enable highly accurate evaluation of the wear state of vehicle tires using a simple configuration and at low cost.

The above-mentioned problem is solved by the tire wear evaluation method of the present invention. Specifically, this evaluation method is a method for evaluating the wear state of vehicle tires, and is characterized by comprising: a target route setting step for setting a target route that serves as a guide for the vehicle when it is automatically traveling; a traveling trajectory acquisition step for acquiring the traveling trajectory of the vehicle when it is automatically traveling from vehicle position data obtained by a satellite positioning system; and a wear evaluation step for evaluating the tire wear state based on the deviation between a curve traveling trajectory in a curved region of the traveling trajectory and a target curve route in a curved region of the target route.

The inventors noted that when a vehicle autonomously navigates a curved section of a predetermined target route, the more advanced the tire wear, the smaller the frictional force generated between the vehicle and the road surface toward the center of the curve, causing the vehicle to travel a more detour than the expected trajectory, i.e., a trajectory that follows the target route. They also noted a strong correlation between the amount of deviation of the actual travel trajectory from the target route and the state of tire wear. The present invention was developed in light of these findings, and evaluates the state of tire wear based on the amount of deviation between the vehicle's travel trajectory in curved sections and the target route. Because the travel trajectory is obtained based on accurate position data measured using a satellite positioning system such as GPS, tire wear can be evaluated with high accuracy based on the deviation between the travel trajectory and the target route. Furthermore, because the travel trajectory is obtained using existing position measurement means (satellite positioning systems) required for autonomous driving, tire wear can be evaluated without the need for additional sensors or other devices. This makes it possible to evaluate tire wear with a simple configuration and at low cost. Furthermore, this method allows tire wear to be evaluated during normal vehicle driving, eliminating the need to set aside time to evaluate tire wear, making it possible to evaluate tire wear extremely efficiently.

In addition, in the tire wear condition evaluation method according to the present invention, the wear condition evaluation step may acquire the shortest distance from each of multiple points on the vehicle's curve driving trajectory to the target curve path, and evaluate the tire wear condition by using the value of the longest shortest distance among the acquired multiple shortest distances as the deviation amount.

In this way, the shortest distance from a point on the curve driving trajectory to the curve target route is the distance at the point where the driving trajectory bulges out the most from the target route (see Figure 9, described below). Therefore, by evaluating the tire wear condition using the maximum value of this shortest distance as the deviation amount, it is possible to more accurately evaluate the tire wear condition.

In addition, in the tire wear condition evaluation method according to the present invention, the wear condition evaluation step may acquire the area of the portion enclosed by the curve driving trajectory and the curve target route, and use the acquired area value as the deviation amount to evaluate the tire wear condition.

In this way, tire wear can be more accurately evaluated by using the area value of the portion enclosed by the curve driving trajectory and the target curve route as the deviation amount. Furthermore, unlike the method of using the maximum value of the shortest distance as the deviation amount described above, this method can reflect all areas where greater than expected skidding occurred due to wear. Therefore, depending on the shape of the driving trajectory, tire wear can be evaluated more accurately than when the shortest distance described above is used as the deviation amount. Furthermore, by evaluating the wear state using the maximum value of the shortest distance described above as the deviation amount (first deviation amount) and evaluating the wear state using the area enclosed by the driving trajectory and the target route as the deviation amount (second deviation amount), more reliable evaluation results for tire wear can be obtained.

The tire wear condition evaluation method according to the present invention may further include a road surface condition evaluation step of capturing an image of a portion of the road surface where a curved driving trajectory is generated and evaluating the condition of the road surface from the captured image of the road surface, and the tire wear condition may be evaluated based on the evaluated road surface condition in the wear condition evaluation step.

In this way, by evaluating tire wear based on the road surface conditions obtained by capturing images of the road surface on which the vehicle is actually traveling, it is possible to more accurately evaluate tire wear by taking into account the effect that road surface conditions have on tire skidding (for example, a decrease in the coefficient of friction between the tire and road surface due to a wet road surface caused by rain). Furthermore, to improve safety, autonomous vehicles may be equipped with cameras to capture images of the vehicle's surroundings. Therefore, by capturing images of the road surface using these existing cameras, it is possible to evaluate tire wear while taking into account the above-mentioned road surface conditions, without increasing the complexity, size, and cost of the equipment.

The tire wear condition evaluation method according to the present invention may further include a road surface condition evaluation step of capturing an image of a portion of the road surface where a curved driving trajectory is generated and evaluating the condition of the road surface from the image of the road surface obtained by capturing the image, and the wear condition evaluation step may determine whether or not evaluation of the tire wear condition is necessary based on the evaluated road surface condition.

The present invention makes it possible to evaluate the state of tire wear by taking advantage of the fact that the frictional resistance between the tire and road surface when traveling around a curve changes (in most cases, decreases) due to tire wear. However, there can be cases where it is extremely difficult to quantitatively evaluate the effect of road surface conditions on the sliding resistance between the tire and road surface, such as when puddles are scattered on the road surface and the road surface condition fluctuates significantly during travel, or when the road surface is extremely hot due to a drought. Here, as described above, by determining whether or not to evaluate the state of tire wear based on the state of the road surface obtained by imaging, it is possible to avoid evaluation when the road surface condition is unstable and there is little chance of obtaining a reliable evaluation result. Therefore, by obtaining an evaluation of the state of tire wear when the road surface condition is stable, it is possible to consistently obtain reliable evaluation results.

The above-mentioned problem can also be solved by a tire wear condition evaluation device according to the present invention. Specifically, this evaluation device is characterized by including a target route setting unit capable of setting a target route to be followed by the vehicle when it is traveling autonomously; a travel trajectory acquisition unit capable of acquiring the travel trajectory of the vehicle when it is traveling autonomously from vehicle position data obtained by a satellite positioning system; and a wear condition evaluation unit capable of evaluating the tire wear condition based on the deviation between a curved travel trajectory in a curved region of the travel trajectory and a target curved route in a curved region of the target route.

The tire wear evaluation device according to the present invention also evaluates tire wear based on the deviation between the vehicle's driving path and the target route in curved areas, allowing for highly accurate evaluation of tire wear. Furthermore, because the driving path is obtained using existing position measurement means (satellite positioning system) during automated vehicle driving, tire wear can be evaluated without the need for additional sensors. This makes it possible to evaluate tire wear with a simple configuration and at low cost. Of course, this device can evaluate tire wear during normal automated vehicle driving, eliminating the need to set aside time to evaluate tire wear, allowing for extremely efficient tire wear evaluation.

As described above, the present invention makes it possible to evaluate the wear state of vehicle tires with high accuracy using a simple configuration and at low cost.

1 is a diagram showing the overall configuration of an automatic vehicle transport system according to an embodiment of the present invention; FIG. 2 is a side view of the automatic transport device shown in FIG. 1 . FIG. 2 is a plan view of the automatic transport device shown in FIG. 1 . FIG. 2 is a front view of the automatic transport device shown in FIG. 1 . 2 is a side view showing a state in which a front wheel of a completed vehicle is mounted on the automatic conveying device shown in FIG. 1 . FIG. 2 is a diagram for conceptually explaining the configuration of a tire wear state evaluation device provided in the automatic conveying device shown in FIG. 1. FIG. 10 is a plan view for conceptually explaining the balance of forces in an automatic guided vehicle when traveling around a curve. 10 is a graph showing the relationship between the speed of an automatic transport device and the amount of deviation. FIG. 10 is a plan view for conceptually explaining the shortest distance from a point on a curve travel locus to a curve target route. FIG. 10 is a plan view for conceptually explaining the area of a portion surrounded by a curve travel locus and a curve target route. FIG. 2 is a plan view for conceptually explaining the curve radius of a curved travel locus. FIG. 10 is a plan view for conceptually explaining the deviation angle between the traveling direction at a point on a curve traveling locus and the traveling direction at a corresponding point on a curve target route.

The following describes an automatic transport device equipped with a tire wear condition evaluation device according to one embodiment of the present invention, and an automatic vehicle transport system equipped with this automatic transport device, with reference to the accompanying drawings.

Figure 1 shows the overall configuration of an automated vehicle transport system 10 according to one embodiment of the present invention. This automated transport system 10 transports completed vehicles C completed in a factory F to a container yard Y, which is a vehicle waiting area, and mainly comprises multiple automated transport devices 11 capable of automatic driving, a control unit 12 that controls the drive of the multiple automated transport devices 11, and a wear condition evaluation device 27 (see Figure 6). The automated transport devices 11 here correspond to vehicles according to the present invention. In this embodiment, the left and right front wheels FW (see Figure 5, described below) of a front-wheel drive completed vehicle C are mounted on the automated transport device 11, and the completed vehicle C is transported with its left and right rear wheels RW (see Figure 5, described below) in contact with the ground. Details will be explained below as an example.

As shown in Figures 2 to 4, the automated transport device 11 has two drive wheels 13, a power applying unit 14 that applies power to each drive wheel 13, a mounting unit 15 capable of mounting the front wheels FW of a completed vehicle C, a GPS (Global Navigation Satellite System) receiving unit 16, and a detection unit 17. In this embodiment, each drive wheel 13 is housed in a casing 18. These two casings 18 are connected to each other by a connecting unit 19. In this case, the mounting units 15 are provided at predetermined widthwise positions on the connecting unit 19, i.e., at two widthwise positions corresponding to the front wheels FW of the completed vehicle C to be mounted. Therefore, in this case, the mounting unit 15 is disposed between the two drive wheels 13. In other words, the mounting unit 15 is disposed in a position that overlaps with the two drive wheels 13 in the fore-and-aft direction of the vehicle body (see Figure 3). The width direction here refers to the direction perpendicular to the fore-and-aft direction of the vehicle body when the completed vehicle C is mounted, which corresponds to the direction in which the two drive wheels 13 of the automatic transport device 11 are separated from each other. In this embodiment, the object to be transported by the automatic transport device 11 is a completed vehicle C, but this is not of course limited to this. For example, the object to be transported may be a mass-produced vehicle that does not have an open loading platform or box-shaped cargo compartment of a light truck, in other words, a vehicle in an unmounted state (a vehicle before mounting).

In this embodiment, each drive wheel 13 is composed of two wheels 20 arranged in parallel to each other, as shown in Figures 3 and 4. Each wheel 20 is rotatable independently of the other and is rotatably supported on a rotation shaft 21 disposed between the wheels 20. The rotation shaft 21 is disposed with its longitudinal direction aligned with the vertical direction when the automated transport device 11 is traveling. Therefore, for example, by rotating the two wheels 20 in opposite directions or by driving only one wheel 20, the drive wheel 13 having the two wheels 20 rotates around the rotation shaft 21, enabling steering of the automated transport device 11. In this embodiment, the two wheels 20 constituting the drive wheels 13 are rotatable at least 90 degrees (preferably 360 degrees) around the rotation shaft 21. Therefore, for example, by rotating these two wheels 20 by 90 degrees (not shown), the direction of travel of the automated transport device 11 can be changed from the fore-and-aft direction of the vehicle body to the width direction.

In this embodiment, as shown in FIG. 3, the power applying unit 14 is provided in the same number as the wheels 20 and is composed of multiple in-wheel motors 22 that apply rotational driving force to each wheel 20. Each in-wheel motor 22 has, for example, a stator and a rotor (not shown), with the stator fixed to the rotation shaft 21 and the rotor connected to the wheel 20. As a result, by driving the rotor of the in-wheel motor 22, the wheel 20 connected to the rotor can rotate together with the rotor. Furthermore, each in-wheel motor 22 can be electrically controlled independently. By configuring the power applying unit 14 as described above, the two wheels 20 arranged in parallel can be driven independently, and the drive wheels 13 can also be driven independently to rotate about both vertical and horizontal axes.

In this embodiment, training wheels 23 are disposed on the vehicle body front side of the connecting portion 19. In this case, the training wheels 23 are capable of contacting the ground further forward on the vehicle body of the automatic transport device 11 than the respective drive wheels 13, and rotate (roll relative to the ground) passively in response to the rotational drive of the drive wheels 13 in a ground contact state. Alternatively, as described below, when the automatic transport device 11 travels with the front wheels FW of the completed vehicle C mounted on the mounting portion 15, the training wheels 23 rotate passively in response to the rotational drive of the drive wheels 13 in a ground contact state.

The receiver 16 is capable of receiving signals from multiple satellites (not shown) for a satellite positioning system. By performing a predetermined calculation based on the received signals, it is possible to obtain the position on Earth of the completed vehicle C (of the receiver 16) at the time of reception. The calculation for obtaining the position may be performed by the receiver 16 or by the control unit 12 (specifically, the terminal control unit 24 or the integrated control unit 25, described below). The receiver 16 may be attached to any position relative to the automated guided vehicle 11. For example, to ensure smooth communication with satellites for the satellite positioning system (positioning satellites), it is preferable to attach the receiver 16 as high as possible on the automated guided vehicle 11. In this embodiment, the receiver 16 is disposed at the tip (top end) of an upright portion 26 that extends from the top surface of the casing 18 (see Figure 2, etc.).

The detection unit 17 is provided at a predetermined position on the automatic transport device 11. This detection unit 17 is used to accurately determine spatial information around the automatic transport device 11 (such as the presence or absence of approaching objects), or to accurately determine the position of a predetermined part (e.g., the front wheels FW) of the completed vehicle C to be transported. In this embodiment, the detection unit 17 is an image acquisition device such as an optical camera or infrared camera, and is capable of capturing images of the road surface R along which the automatic transport device 11 is automatically traveling.

The control unit 12 controls the two drive wheels 13 and the power applying unit 14, enabling the automatic guided vehicle 11 to travel automatically with steering. In this embodiment, the control unit 12 is composed of multiple terminal control units 24 provided in each automatic guided vehicle 11 and an overall control unit 25 that communicates with these multiple terminal control units 24. Here, the terminal control unit 24 controls the drive wheels 13 and the power applying unit 14 based on commands from the overall control unit 25, position information (position data) of the automatic guided vehicle 11 obtained by the satellite positioning system via the receiving unit 16, information about the target route TR (see Figure 1) that serves as the target for automatic travel, and spatial information about the surroundings of the automatic guided vehicle 11 obtained by the detection unit 17, thereby enabling the automatic guided vehicle 11 to travel automatically with steering. In other words, the terminal control unit 24 can timely control the steering angle and speed (including acceleration, deceleration, and stopping) of the automatic guided vehicle 11 based on the commands, position information, etc.

In the above case, from the viewpoint of facilitating control by the control unit 12, it is desirable that the power applying unit 14 be an electrically driven device such as a motor. Furthermore, if the automatic transport device 11 is provided with a mechanism separate from the power applying unit 14 that performs the operations necessary for loading the completed vehicle C and transporting it in its loaded state, it is desirable that this mechanism be an electrically driven mechanism for the same reasons as the power applying unit 14.

As shown in FIG. 6, the wear condition evaluation device 27 includes a target route setting unit 28, a driving trajectory acquisition unit 29, and a wear condition evaluation unit 30. In this embodiment, the wear condition evaluation device 27 further includes a road surface condition evaluation unit 31, and this wear condition evaluation device 27 is incorporated into the terminal control unit 24.

The target route setting unit 28 is configured to be able to set a target route TR (see Figure 1) that will be the target when the automated guided vehicle 11 travels automatically. It is also configured to be able to store information about the set target route TR, such as the position information of multiple target points that make up the target route TR. The target route setting unit 28 may be provided in the overall control unit 25, in which case the terminal control unit 24 is configured to be able to store the position information of the set target route TR.

The travel trajectory acquisition unit 29 is configured to be able to acquire the actual travel trajectory P (see Figure 7) of the automatic guided vehicle 11 as it automatically travels along the target route TR from the position data of the automatic guided vehicle 11 obtained by the satellite positioning system. In this case, the travel trajectory P can be acquired, for example, as a collection of position data of the automatic guided vehicle 11 at predetermined time intervals obtained by the satellite positioning system via the receiving unit 16, or as an approximate straight line or curve passing through the coordinates associated with these multiple position data.

As shown in FIG. 7, the wear condition evaluation unit 30 is configured to evaluate the wear condition of the tire 20a (see FIG. 2) of the wheel 20 based on the deviation D between the curve driving locus Pc in a predetermined curve region Rc of the driving locus P and the curve target route TRc in the curve region Rc of the target route TR. That is, the wear condition evaluation unit 30 calculates the deviation D between the curve driving locus Pc and the curve target route TRc based on information about the curve driving locus Pc acquired by the driving locus acquisition unit 29 and information about the curve target route TRc set by the target route setting unit 28. The wear condition of the tire 20a is then evaluated based on the calculated deviation D.

Next, the relationship between the amount of deviation D and the speed V of the automatic conveying device 11 will be explained with reference to Figures 7 and 8.

When the automated guided vehicle 11 automatically travels along the target route TR, the control unit 12 (here, the terminal control unit 24) controls the steering angle and speed V of the automated guided vehicle 11 based on the position information of the automated guided vehicle 11 and position information related to the target route TR. That is, the control unit 12 controls the movement direction and speed V of the automated guided vehicle 11 so that the automated guided vehicle 11 automatically travels along the same target route TR at the same speed V each time, based on a preset profile of the target route TR and speed V. Therefore, as shown in FIG. 7 , even in a curved region Rc where centrifugal force tends to cause a large turn, the automated guided vehicle 11 can travel automatically with almost no deviation (deviation amount D) between the actual curved travel path Pc and the curved target route TRc. The speed V of the automated guided vehicle 11 can be detected directly or indirectly using known speed measurement means, such as a speed sensor for the wheels 20 or a rotation speed measurement device for the motor (in-wheel motor 22) that rotates the wheels 20.

Here, let us consider the balance of forces when traveling around a curve. As shown in Fig. 7, when traveling on a curved road surface R, a centrifugal force Fc acts on the automated guided vehicle 11 in a direction away from the center O of the curve, and a frictional force Ff acts on the automated guided vehicle 11 in a direction toward the center O of the curve, balancing the centrifugal force Fc. Here, the centrifugal force Fc can be expressed as a function of the speed V of the automated guided vehicle 11 (see Equation 1). Furthermore, the frictional force Ff can be expressed as a function of the coefficient of friction between the tire 20a and the road surface R (here, the static friction coefficient μ) (see Equation 2).

In Equation 1, m represents the weight of the automatic conveying device 11 taking into account the weight of the object to be conveyed (here, the completed vehicle C), and r represents the curve radius.

In Equation 2, μ represents the static friction coefficient of the tire 20a with respect to the road surface R, and g represents the gravitational acceleration.
From Equation 1 and Equation 2, the relationship between the velocity V and the static friction coefficient μ can be expressed as Equation 3.

Equation 3 shows that, assuming that the static friction coefficient μ is constant, the curve target route TRc must be set on the assumption that the curve radius r described by the curve driving trajectory Pc increases as the speed V increases. Conversely, it can be seen that the speed V must be set to an appropriate value to match the curve radius of the curve target route TRc in the curve region Rc.

On the other hand, under certain conditions, the variables μ, g, and r in Equation 3 other than speed V are constant, which indicates that there is a maximum speed Vm at which the balance between centrifugal force Fc and centripetal force (frictional force) Ff is maintained. Therefore, when speed V exceeds maximum speed Vm, centrifugal force Fc exceeds frictional force Ff, causing skidding of the automated guided vehicle 11 while it is traveling automatically through the curved region Rc. In this case, the curved travel trajectory Pc1 (see Figure 7) of the automated guided vehicle 11 traces a curve that is larger than the curve target route TRc. Furthermore, as shown in Figure 8, the greater the value of speed V, the greater the amount of skidding (deviation D). Therefore, the control unit 12 (terminal control unit 24) must set the speed V of the automated guided vehicle 11 to an appropriate value (less than maximum speed Vm) when traveling through the curved region Rc to prevent skidding.

On the other hand, repeated automatic driving (here, automatic transport) of the automatic transport device 11 inevitably causes wear on the tire 20a. As wear progresses, the grip force of the tire 20a on the road surface R decreases, and the friction coefficient with the road surface R (here, the static friction coefficient μ) decreases. In this case, even if the automatic transport device 11 is automatically driven on the target route TR at the same speed as before (for example, the maximum speed Vm at which skidding does not occur), skidding will occur because the centripetal force (friction force) Ff falls below the centrifugal force Fc. As a result, the automatic transport device 11 will automatically drive along a curved driving trajectory Pc2 (see Figure 7), which is a larger detour than the curved target route TRc.

Figure 8 shows the relationship between the speed V of the automated guided vehicle 11 and the amount of sideslip (deviation D) when traveling around a curve. As shown in Figure 8, when the tire 20a is, for example, unused and unworn (initial state), and the tire 20a is automatically driven at the maximum speed Vm1 at which sideslip does not occur, the amount of sideslip (deviation D) is zero (see graph G1 in Figure 8). On the other hand, if the tire 20a is worn through repeated automated driving of the automated guided vehicle 11, the static friction coefficient μ decreases as described above, and graph G1 shifts overall to the left. That is, as shown in graph G2 in Figure 8, the maximum speed Vm at which sideslip does not occur decreases (from Vm1 to Vm2) due to wear, and therefore, if the tire is automatically driven at the same maximum speed Vm1 as before, a corresponding amount of sideslip (deviation) will occur. Therefore, the wear state evaluation unit 30 evaluates the wear state of the tire 20a from the magnitude of this sideslip (deviation D1).

Here, various values can be used for the deviation amount D, and specific examples include the maximum value Em of the shortest distance E from a point on the curve driving trajectory Pc to the curve target route TRc (see Figure 9), the area S of the portion enclosed by the curve driving trajectory Pc and the curve target route TRc (see Figure 10), the maximum value rm of the curve radius r of the curve driving trajectory Pc (see Figure 11), and the maximum value θm of the deviation angle θ in the direction of travel (see Figure 12).

Here, when calculating the deviation amount D as the maximum value Em of the shortest distance E shown in Figure 9, for example, the shortest distance E1 (E2...Ei...) from each of multiple points p1, p2...pi... on the traveling trajectory P to the curve target route TRc is calculated. Then, of the multiple calculated shortest distances E1, E2...Ei..., the largest shortest distance value Em (e.g., Ei) is obtained as the deviation amount D. Note that the method for calculating the shortest distance E1 (E2...Ei...) can be arbitrary. For example, it can be calculated as the straight-line distance between point Ei tangent to the inscribed circle IC with the largest diameter among the inscribed circles of each point p1 (E2...Ei...) tangent to the curve target route TRc as shown in the figure, and a point on the curve target route TRc.

Next, the relationship between the amount of deviation D and the actual amount of wear of the tire 20a is obtained in advance through experiments, etc., and the wear state (amount of wear) of the tire 20a is evaluated from the calculated amount of deviation D (here, for example, the maximum value Em of the shortest distance E) based on this relationship between the amount of deviation D and the amount of wear.

The wear condition evaluation unit 30 may also determine whether or not the tire 20a needs to be replaced based on the wear condition of the tire 20a evaluated as described above (a tire replacement necessity determination step S4, described below). That is, in this determination step, for example, a threshold value may be set in advance for the amount of wear that requires replacement of the tire 20a, and if the evaluated amount of wear is equal to or greater than the threshold value, it may be determined that the tire 20a needs to be replaced, and if the evaluated amount of wear is less than the threshold value, it may be determined that the tire 20a does not need to be replaced.

The above-mentioned tire replacement necessity determination process S4 can also be performed based on the value of the deviation amount D obtained by the wear state evaluation unit 30. In this case, in the tire replacement necessity determination process S4, for example, a threshold value for the deviation amount D corresponding to the amount of wear that requires replacement of the tire 20a is set in advance, and if the obtained deviation amount D is equal to or greater than the threshold value, it can be determined that the tire 20a needs to be replaced, and if the evaluated deviation amount D is less than the threshold value, it can be determined that the tire 20a does not need to be replaced.

Furthermore, when the wear condition evaluation device 27 includes a road surface condition evaluation unit 31, as in this embodiment, the road surface condition evaluation unit 31 may capture an image of the road surface R at a location where the curved driving trajectory Pc is generated, and evaluate the condition of the road surface R from the image of the road surface R obtained by capturing the image (road surface condition evaluation step S5, described below). In this case, the wear condition evaluation unit 30 evaluates the wear condition of the tire 20a based on the condition of the road surface R evaluated by the road surface condition evaluation unit 31. For example, if it is determined from the image that the road surface R is slightly slippery compared to normal, the wear condition of the tire 20a may be evaluated by multiplying the deviation amount D by a coefficient (a value less than 1) related to the condition of the road surface R.

On the other hand, if the condition of the road surface R evaluated by the road surface condition evaluation unit 31 is affected by a sudden event, such as scattering of luggage during transportation, or by a weather-related event, such as extreme heat or prolonged rain, it is possible that the deviation amount D has fluctuated significantly due to factors other than wear of the tire 20a. Therefore, the wear condition evaluation unit 30 may determine whether or not to evaluate the wear condition of the tire 20a based on the evaluation of the condition of the road surface R obtained by the road surface condition evaluation unit 31. In other words, if the wear condition evaluation unit 30 determines (evaluates) that the condition of the road surface R is significantly different from normal, for example, due to scattering of foreign matter, cracks, bulges, puddles, or freezing, the wear condition evaluation unit 30 may determine to avoid evaluating the wear condition of the tire 20a.

Next, an example of the operation of an automatic conveyance system 10 for a completed vehicle C equipped with the automatic conveyance device 11 configured as described above will be explained mainly with reference to Figures 1 to 5, and an example of evaluation of the wear condition by the wear condition evaluation device 27 configured as described above will be explained mainly with reference to Figures 6 to 12.

First, the central control unit 25 sends commands to each of the multiple automated guided vehicles 11 regarding what it should do next. For example, in FIG. 1, the central control unit 25 sends a command to the automated guided vehicle 11 (11a) located between the container yard Y and the factory F, which is empty (i.e., it is not carrying a completed vehicle C), to move toward the factory F. The central control unit 25 also sends a command to the automated guided vehicle 11 (11b) located within the factory F premises to move toward a position where it can carry the completed vehicle C to be transported. The central control unit 25 also sends a command to the automated guided vehicle 11 (11c) located between the factory F and the container yard Y, which is carrying a completed vehicle C, to move along the predetermined target route TR toward a predetermined waiting position within the container yard Y. After unloading, the central control unit 25 sends a command to the automated guided vehicle 11 (11d, 11e) to change its orientation relative to the direction of movement as necessary and then retreat from the container yard Y. Upon receiving the command, the central control unit 24 controls the drive wheels 13 and power applying units 14 of each automated guided vehicle 11 (11a-11e) to operate in accordance with the command. In this way, the automatic travel of multiple automatic transport devices 11 (11a to 11e) and the automatic transport of completed vehicles C by these automatic transport devices 11 (11a to 11e) are continuously carried out.

The target route TR used for the automatic transportation of the completed vehicle C described above is set in advance by the target route setting unit 28 of the wear condition evaluation device 27 (target route setting process S1). Furthermore, upon receiving a command to automatically travel along the target route TR, the automatic transport device 11 acquires the travel route P during automatic travel from the position data of the automatic transport device 11 obtained by the satellite positioning system via the receiver 16, using the travel route acquisition unit 29 of the wear condition evaluation device 27 (travel route acquisition process S2). The terminal control unit 24 then controls the steering angle and speed V of the automatic transport device 11 based on the target route TR set in the target route setting process S1 and the travel route P acquired in the travel route acquisition process S2, so that there is always no deviation between the target route TR and the travel route P. This allows the automatic transport of the automatic transport device 11 to be continuously performed along the target route TR.

In addition, the integrated control unit 25 sends a command to the wear condition evaluation device 27 at a predetermined timing to evaluate the wear condition of the tires 20a of the automatic transport device 11 (11a to 11e) while the automatic transport device 11 is traveling automatically. The wear condition evaluation unit 30 of the wear condition evaluation device 27, which receives the command, evaluates the wear condition of the tires 20a when the automatic transport device 11 travels through a predetermined curve region Rc (see Figure 1) (wear condition evaluation process S3).

Specifically, the travel trajectory acquisition unit 29 acquires the travel trajectory P (curve travel trajectory Pc) when the automated conveying device 11 travels through a specified curve region Rc. Information related to the acquired curve travel trajectory Pc is transmitted to the wear condition evaluation unit 30 or made available for reference. Information related to the curve target route TRc, which is the target route TR in the curve region Rc, is also transmitted to the wear condition evaluation unit 30 or made available for reference.

The wear condition evaluation unit 30 evaluates the wear condition of the tire 20a of the automated guided vehicle 11 based on the deviation D between the curve driving trajectory Pc and the target curve path TRc. Here, the deviation D is calculated as the maximum value Em of the shortest distance E from point p1 (p2...pi...) on the curve driving trajectory Pc to the target curve path TRc. The wear condition (here, the amount of wear) of the tire 20a is then evaluated based on the acquired deviation D and the previously acquired relationship between the deviation D and the wear condition of the tire 20a. Based on the evaluated amount of wear, it is determined whether the tire 20a needs to be replaced (tire replacement necessity determination S4). If the evaluated amount of wear is equal to or greater than the predetermined wear threshold value as described above, it is determined that the tire 20a needs to be replaced. If the evaluated amount of wear is less than the threshold value, it is determined that the tire 20a does not need to be replaced.

If it is determined that the tire 20a needs to be replaced, the automatic transport of the completed vehicle C is immediately stopped, or once the current automatic transport is completed, the completed vehicle C is moved to the tire 20a replacement area and the tire 20a is replaced. If it is determined that the tire 20a does not need to be replaced, the automatic transport of the completed vehicle C continues to be repeated. In this way, the wear state of the tire 20a is evaluated. This wear state evaluation is performed, for example, every time the automatic transport device 11 passes through the curve area Rc a predetermined number of times.

In addition, in this embodiment, the road surface condition evaluation unit 31 of the wear condition evaluation device 27 images the portion of the road surface R where the curved driving locus Pc is generated (see Figure 7) and evaluates the condition of the road surface R obtained by the image (road surface condition evaluation step S5). Then, based on the evaluated state of the road surface R, it is determined whether or not the wear condition evaluation step S3 for the tire 20a is necessary. Here, if it is determined (evaluated) that the evaluated state of the road surface R is not significantly different from normal, the above-mentioned wear condition evaluation step S3 for the tire 20a is performed. On the other hand, if it is determined (evaluated) that the evaluated state of the road surface R is significantly different from normal, as already described, it is determined that evaluation of the wear condition of the tire 20a should be avoided.

As described above, the wear condition evaluation device 27 according to this embodiment evaluates the wear condition of the tire 20a of the automated guided vehicle 11 based on the deviation D between the curve driving trajectory Pc of the automated guided vehicle 11 and the target curve path TRc in a predetermined curve region Rc. By evaluating the wear condition of the tire 20a based on information obtained during actual driving in this manner, the wear condition of the tire 20a can be evaluated with high accuracy. Furthermore, because the driving trajectory P (curve driving trajectory Pc) of the automated guided vehicle 11 is obtained using an existing position measurement means (satellite positioning system) during the automated driving of the automated guided vehicle 11, the wear condition of the tire 20a can be evaluated without installing any additional sensors or the like. This makes it possible to evaluate the wear condition of the tire 20a with a simple configuration and at low cost. Of course, since the wear condition evaluation device 27 can evaluate the wear condition of the tire 20a during normal automated driving of the automated guided vehicle 11, there is no need to set aside time to evaluate the wear condition of the tire 20a. This enables extremely efficient evaluation of the wear condition of the tire 20a.

In this embodiment, in the wear state evaluation step S3, the shortest distance E1 (E2...Ei...) from each of multiple points p1, p2...pi... on the curve driving trajectory Pc of the automated conveying device 11 to the target curve path TRc is acquired, and the wear state of the tire 20a is evaluated using the largest shortest distance value Em among the acquired multiple shortest distances E1, E2...Ei... as the deviation amount D (see FIG. 9 ). When the deviation amount D is evaluated in this manner, the shortest distance E1 (E2...Ei...) from a point p1 (p2...pi...) on the curve driving trajectory Pc to the target curve path TRc is the longest at the point where the curve driving trajectory Pc bulges most greatly with respect to the target curve path TRc. Therefore, by evaluating the wear state of the tire 20a using the maximum value Em of this shortest distance as the deviation amount D, it is possible to more accurately evaluate the wear state of the tire 20a.

In addition, this embodiment further includes a road surface condition evaluation step S5 in which the portion of the road surface R where the curved driving trajectory Pc is generated is imaged and the condition of the road surface R is evaluated from the image of the road surface R. In addition, the wear condition evaluation step S3 determines whether or not to evaluate the wear condition of the tire 20a based on the condition of the road surface R evaluated in the road surface condition evaluation step S5. In this way, by determining whether or not to evaluate the wear condition of the tire 20a based on the condition of the road surface R obtained by image capture, evaluation can be avoided when the condition of the road surface R is unstable and a reliable evaluation result is unlikely to be obtained. Therefore, by obtaining an evaluation of the wear condition of the tire 20a only when it is determined that the condition of the road surface R is stable (unchanging from normal conditions), it is possible to always obtain reliable evaluation results. This enables stable automated driving, and ultimately automatic transportation of the completed vehicle C, to be performed consistently and safely.

The above describes one embodiment of the present invention, but the wear condition evaluation method and wear condition evaluation device according to the present invention can also be configured in other ways without departing from the spirit of the invention.

For example, in the above embodiment, the maximum value Em (see FIG. 9) of the shortest distance E from a point on the curve driving trajectory Pc to the curve target route TRc is used as the deviation amount D to evaluate the wear state of the tire 20a, but this is of course not limited to this. Various parameters can be used, such as the area S (see FIG. 10) of the portion surrounded by the curve driving trajectory Pc and the curve target route TRc, the maximum value rm (see FIG. 11) of the curve radius r of the curve driving trajectory Pc, and the maximum value θm (see FIG. 12) of the deviation angle θ in the traveling direction.

Furthermore, the wear state of tire 20a may be evaluated using two or more of the multiple parameters Em, S, rm, and θm described above (for example, the maximum value Em of the shortest distance E and the area S). By evaluating the wear state of tire 20a based on multiple parameters, more stable evaluation results can be obtained, and the reliability of the evaluation results can be further improved.

In addition, in the above embodiment, an example was given of a case in which the need for tire replacement 20a was determined based on the wear state (amount of wear) of the tire 20a evaluated in the wear state evaluation step S3 (tire replacement need determination step S4), but it is of course possible to use the evaluation results regarding the wear state in other ways. For example, although not shown in the figures, a speed adjustment step S6 may be further provided in which the speed V (more precisely, the maximum value Vm of the speed V) of the automatic conveying device 11 when traveling through the curve region Rc is adjusted based on the wear state of the tire 20a evaluated in the wear state evaluation step S3.

In addition, in the above embodiment, the wear state of the tire 20a evaluated in the wear state evaluation step S3 is the amount of wear of the tire 20a, but this is not necessarily limited to this. For example, although not shown in the figures, it is also possible to evaluate the wear area of the tire 20a (such as the area ratio of the worn area to the entire surface of the tire 20a) as one aspect of the wear state.

In addition, while the above embodiment illustrates a case in which the wear state of tire 20a is evaluated based on the amount of deviation D and the state of road surface R, this is not necessarily limited to this. For example, in addition to the amount of deviation D and the state of road surface R, the force that tire 20a receives from road surface R may be detected as a load on the steering motor, and this detected force may also be taken into consideration when evaluating the wear state of tire 20a. Alternatively, the temperature of tire 20a may be detected, and the detected temperature of tire 20a may also be taken into consideration when evaluating the wear state of tire 20a.

In addition, in the above embodiment, the deviation amount D of the automated guided vehicle 11 in the curve region Rc (see FIG. 7 ) that curves in a fixed direction is evaluated, and the wear state of all tires 20a in contact with the road surface R is evaluated based on the evaluated deviation amount D. However, the wear state of the tires 20a can also be evaluated in other ways. For example, although not shown in the figures, the deviation amount D is evaluated as described above in a first curve region that curves to the left and a second curve region that curves to the right. Then, by evaluating the wear state of the tires 20a based on each deviation amount D and comparing the deviation amount D in the first curve region with the deviation amount D in the second curve region, it is possible to comprehensively evaluate the wear state of the tires 20a as a whole, while simultaneously evaluating which of the left and right tires 20a is more worn (whether there is a wear imbalance).

In addition, while the above explanation exemplifies a case in which the control unit 12 is configured with the terminal control unit 24 and the overall control unit 25, this is not necessarily limited to this. For example, the overall control unit 25 may be omitted, and the automatic travel of the automatic transport device 11 may be controlled solely by the terminal control unit 24. In this case, for example, for the automatic transport device 11, a program related to automatic transport involving loading and unloading may be stored in advance in the terminal control unit 24, and the drive wheels 13 and power applying unit 14 may be driven and controlled based on the program through predetermined operations by an operator.

Furthermore, in the above explanation, an example was given in which the drive unit of the automatic transport device 11 was configured with two drive wheels 13, but of course this is not limited to this. Although not shown in the figures, the drive unit may also be configured with three or four or more drive wheels 13. Similarly, in the above explanation, an example was given in which each drive wheel 13 was configured with two wheels 20 arranged in parallel, but of course other configurations are also possible. Depending on the number of drive wheels 13, the drive wheel 13 may be configured with a single wheel 20.

In addition, while the above description has been given with an example in which multiple in-wheel motors 22 are provided as the power supply unit 14, this is of course not limited to this. As long as a predetermined power (rotational driving force) can be provided to the drive wheels 13, any drive source configuration can be provided as the power supply unit 14 in the automatic transport device 11.

While the above embodiment illustrates a loading operation in which the front wheels FW of the completed vehicle C are loaded onto the automated transporter 11 by moving (e.g., moving forward) the completed vehicle C relative to the stopped automated transporter 11, this is not necessarily limited to this. For example, although not illustrated, the automated transporter 11 may be moved to guide the front wheels FW of the stopped completed vehicle C onto the coupling 19, thereby loading the front wheels FW onto the automated transporter 11. Alternatively, although not illustrated, a self-propelled lift-up device manufactured separately from the automated transporter 11 may be inserted beneath the front of the completed vehicle C to lift up the front side of the stopped completed vehicle C, and then the automated transporter 11 may be moved to load the front wheels FW onto the automated transporter 11. Essentially, any means is possible as long as the front wheels FW can be loaded onto the automated transporter 11. Of course, the above-described points may also be applied to loading rear wheels RW, rather than front wheels FW, onto the automated transporter 11.

In addition, while the above explanation exemplifies a case in which the tire 20a of the automated conveying device 11 is used as the subject of evaluation of the wear state (subject of application of the present invention), this is not limited to this. For example, the tire of an autonomous vehicle that is the subject of a durability test may also be used as the subject of evaluation by the evaluation method and evaluation device of the present invention. Of course, the subject of evaluation is not limited to vehicles capable of autonomous driving, and the present invention can also be applied to tires of ordinary vehicles driven by occupants.

10 Automatic transport system 11 Automatic transport device 12 Control unit 13 Drive wheel 14 Power supply unit 15 Mounting unit 16 Receiving unit 17 Detection unit 18 Casing 19 Connecting unit 20 Wheel 20a Tire 21 Rotating shaft 22 In-wheel motor 23 Auxiliary wheel 24 Terminal control unit 25 General control unit 26 Standing unit 27 Wear state evaluation device 28 Target route setting unit 29 Traveling trajectory acquisition unit 30 Wear state evaluation unit 31 Road surface condition evaluation unit C Completed vehicle D Deviation amount E Shortest distance F Factory Fc Centrifugal force Ff Friction force FW Front wheel RW Rear wheel IC Inscribed circle P Traveling trajectory Pc, Pc1, Pc2 Curve traveling trajectory r Curve radius R Road surface Rc Curve area S Area TR Target route TRc Curve target route V Speed Y Container yard θ Deviation angle

Claims (3)

1. A method for assessing the wear state of a tire of a vehicle, comprising:
a target route setting step of setting a target route that is a target when the vehicle is automatically traveling;
a travel trajectory acquisition step of acquiring a travel trajectory of the vehicle when the vehicle is automatically traveling from position data of the vehicle obtained by a satellite positioning system;
a correlation acquisition step of acquiring a correlation between a deviation amount between a curve driving locus in a curve region of the driving locus and a curve target route in the curve region of the target route, and a wear state of the tire;
a wear state evaluation step of evaluating the wear state of the tire based on the deviation amount and the correlation . The wear condition evaluation method described in claim 1, wherein the wear condition evaluation step acquires the shortest distance from each of multiple points on the curve driving trajectory of the vehicle to the curve target path, and evaluates the tire wear condition by using the largest of the acquired shortest distances as the deviation amount. a target route setting unit that can set a target route that will be a target when the vehicle is automatically traveling;
a travel locus acquisition unit capable of acquiring a travel locus of the vehicle when the vehicle is traveling automatically from position data of the vehicle obtained by a satellite positioning system;
a wear condition evaluation unit that acquires in advance a correlation between a curve driving locus in a curve region of the driving locus and a curve target route in the curve region of the target route, and the tire wear condition, and evaluates the tire wear condition based on the newly calculated deviation amount based on the driving locus acquired by the driving locus acquisition unit and the previously acquired correlation .