Estimation system, estimation method, and estimation program

Abstract

To estimate a state of a rotor by a simple configuration.SOLUTION: An estimation system comprises: a first sensor that can be arranged between a wheel and a tyre mounted to the wheel, and outputs a first sensor signal corresponding to pressing force by the wheel and tyre; and a processor that estimates a state of a rotor including the wheel and tyre on the basis of the first sensor signal. The processor is configured to generate a first section signal by dividing the first sensor signal in a specific section, and estimate the state of the rotor on the basis of the first section signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an estimation system, an estimation method, and an estimation program. [Background technology]

[0002] There are known techniques for estimating the condition of a vehicle tire. For example, Patent Document 1 describes a technique for measuring the camber angle of a tire using two laser devices spaced apart on the outside of an automobile tire / wheel assembly. Patent Document 2 describes a technique for estimating the load acting on a tire using an acceleration sensor provided in the inner liner of the tire and located at the center of the tire in the width direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-247745 [Patent Document 2] Japanese Patent Application Publication No. 2019-49488 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 requires a laser device to be attached to the outside of the tire, which makes the device bulky and may interfere with vehicle movement.The technology described in Patent Document 2 requires a dedicated tire with an acceleration sensor attached to the inner liner.

[0005] The present disclosure describes an estimation system, an estimation method, and an estimation program that are capable of estimating the state of a rotating body with a simple configuration. [Means for solving the problem]

[0006] An estimation system according to one aspect of the present disclosure includes a first sensor that can be arranged between a wheel and a tire mounted on the wheel and outputs a first sensor signal corresponding to a pressing force between the wheel and the tire, and a processor that estimates the state of a rotating body including the wheel and the tire based on the first sensor signal. The processor generates a first section signal by dividing the first sensor signal into specific sections, and estimates the state of the rotating body based on the first section signal.

[0007] An estimation method according to another aspect of the present disclosure includes obtaining a sensor signal corresponding to the pressing force exerted by the wheel and the tire from a sensor disposed between the wheel and the tire mounted on the wheel, generating a section signal by dividing the sensor signal into specific sections, and estimating the state of the rotating body including the wheel and the tire based on the section signal.

[0008] An estimation program according to yet another aspect of the present disclosure includes instructions for causing a computer to acquire a sensor signal corresponding to the pressing force exerted by the wheel and the tire from a sensor disposed between the wheel and the tire mounted on the wheel, generate a section signal by dividing the sensor signal into specific sections, and estimate the state of a rotating body including the wheel and the tire based on the section signal. [Effects of the Invention]

[0009] According to each aspect and embodiment of the present disclosure, the state of a rotating body can be estimated with a simple configuration. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram schematically illustrating a vehicle equipped with an estimation system according to an embodiment. [Figure 2] FIG. 2 is a perspective view of the rotating body shown in FIG. [Figure 3] FIG. 3 is a diagram schematically illustrating the configuration of the estimation system shown in FIG. [Figure 4]FIG. 4 is an exploded perspective view of the sensor module shown in FIG. [Figure 5] FIG. 5 is a diagram for explaining forces acting on the sensor module shown in FIG. [Figure 6] FIG. 6 is a diagram for explaining a sensor signal output from the sensor shown in FIG. [Figure 7] FIG. 7 is a diagram showing an example of a sensor signal when the vehicle is traveling at a constant speed. [Figure 8] FIG. 8 is a diagram showing an example of a sensor signal during acceleration. [Figure 9] FIG. 9 is a flowchart showing an estimation method performed by the processor shown in FIG. [Figure 10] FIG. 10 is a diagram for explaining an example of the process of generating the section signal. [Figure 11] FIG. 11 is a diagram for explaining another example of the process of generating the section signal. [Figure 12] FIG. 12 is a diagram for explaining yet another example of the process of generating the section signal. [Figure 13] FIG. 13 is a diagram for explaining yet another example of the process of generating the section signal. [Figure 14] FIG. 14 is a diagram for explaining the reaction force from the road surface when the camber angle is 0 degrees. [Figure 15] FIG. 15 is a diagram for explaining the reaction force from the road surface in a positive camber state. [Figure 16] FIG. 16 is a diagram for explaining the reaction force from the road surface in a negative camber. [Figure 17] FIG. 17 is a diagram showing an example of the sensor signal for each camber angle. [Figure 18] FIG. 18 is a diagram for explaining the slip angle. [Figure 19] FIG. 19 is a diagram for explaining the force acting on the sensor module when a slip angle occurs. [Figure 20] FIG. 20 is a diagram showing an example of the sensor signal for each slip angle. [Figure 21]FIG. 21 is a diagram for explaining the peak-to-peak value and the second peak value. [Figure 22] FIG. 22 is a diagram showing the relationship between the peak-to-peak value and the damping rate when the slip angle, camber angle, load, and air pressure are changed. [Figure 23] FIG. 23 is a partially enlarged view of FIG. [Figure 24] FIG. 24 is a diagram for explaining the estimation model. [Figure 25] FIG. 25 is a diagram illustrating a configuration of an estimation system according to another embodiment. [Figure 26] FIG. 26 is a diagram showing an example of the arrangement of sensor modules. [Figure 27] FIG. 27 is a diagram showing an example of the sensor signal for each camber angle. [Figure 28] FIG. 28 is a diagram showing an example of the sensor signal for each slip angle. [Figure 29] FIG. 29 is a diagram illustrating a configuration of an estimation system according to yet another embodiment. [Figure 30] FIG. 30 is a diagram illustrating a configuration of an estimation system according to yet another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] [1] Overview of the embodiment An estimation system according to one aspect of the present disclosure includes a first sensor that can be arranged between a wheel and a tire mounted on the wheel and outputs a first sensor signal corresponding to a pressing force between the wheel and the tire, and a processor that estimates the state of a rotating body including the wheel and the tire based on the first sensor signal. The processor generates a first section signal by dividing the first sensor signal into specific sections, and estimates the state of the rotating body based on the first section signal.

[0012] An estimation method according to another aspect of the present disclosure includes obtaining a sensor signal corresponding to the pressing force exerted by the wheel and the tire from a sensor disposed between the wheel and the tire mounted on the wheel, generating a section signal by dividing the sensor signal into specific sections, and estimating the state of the rotating body including the wheel and the tire based on the section signal.

[0013] An estimation program according to yet another aspect of the present disclosure includes instructions for causing a computer to acquire a sensor signal corresponding to the pressing force exerted by the wheel and the tire from a sensor disposed between the wheel and the tire mounted on the wheel, generate a section signal by dividing the sensor signal into specific sections, and estimate the state of a rotating body including the wheel and the tire based on the section signal.

[0014] In the technology according to the present disclosure, which includes these estimation systems, estimation methods, and estimation programs (hereinafter, sometimes simply referred to as "the technology according to the present disclosure"), a sensor (first sensor) disposed between a wheel and a tire is configured to output a sensor signal (first sensor signal) corresponding to the pressing force exerted by the wheel and the tire. A load from the vehicle acts on the sensor (first sensor) via the wheel. A reaction force from the road surface acts on the sensor (first sensor) via the tire. These forces can change depending on the state of the rotating body, so the technology according to the present disclosure makes it possible to estimate the state of the rotating body based on the sensor signal (first sensor signal). Therefore, the technology according to the present disclosure makes it possible to estimate the state of the rotating body with a simple configuration in which a sensor (first sensor) is disposed between the wheel and the tire.

[0015] In some embodiments, the first sensor may be disposed between a rim and a tire included in a wheel. When a wheel includes a rim, the tire is mounted on the rim. Therefore, the state of the rotating body can be estimated by a simple configuration in which the first sensor is disposed between the rim and the tire.

[0016] In some embodiments, the rotating body may include a first end and a second end, which are opposite ends of the rotating body in the direction of the rotation axis. The first sensor may be disposed at a position closer to the first end than to the center of the rotating body in the direction of the rotation axis. If the first sensor is disposed at the center of the rotating body in the direction of the rotation axis, for example, the first sensor signal changes in the same manner regardless of whether the camber angle changes in the positive direction or the negative direction. On the other hand, in the above configuration, the first sensor signal changes asymmetrically. Therefore, it is possible to improve the accuracy of estimating the state of the rotating body.

[0017] In some embodiments, the estimation system may further include a second sensor that can be disposed between the wheel and the tire and that outputs a second sensor signal corresponding to the pressing force between the wheel and the tire. The second sensor may be disposed at a position closer to the second end than the center of the rotating body in the rotational axis direction. The processor may generate a second-section signal by dividing the second sensor signal into specific sections and estimate the state based on the second-section signal. In this case, the first sensor and the second sensor are disposed on opposite sides of the center of the rotating body in the rotational axis direction. The first sensor signal output from the first sensor and the second sensor signal output from the second sensor change differently in response to changes in the state of the rotating body. Therefore, the state of the rotating body is estimated using two sensor signals that change differently, which enables improved estimation accuracy of the state of the rotating body compared to a configuration in which the state of the rotating body is estimated using a single sensor signal.

[0018] In some embodiments, the specific section may be a section corresponding to one rotation of the rotating body. As the rotating body rotates, the portion of the rotating body that contacts the road surface changes, and the relative positional relationship between the first sensor and the contact portion changes. Therefore, the first sensor signal has a periodicity in which the waveform shape is the same for each rotation of the rotating body. Therefore, by analyzing the first section signal corresponding to one rotation of the rotating body, it is possible to estimate the state of the rotating body.

[0019] In some embodiments, the processor may estimate the state of the rotating body based on a plurality of different waveform characteristics calculated from the first-section signal. The waveform characteristics calculated from the first-section signal can be indicators representing the state of the rotating body. Therefore, by using these characteristics, it is possible to improve the accuracy of estimating the state of the rotating body.

[0020] In some embodiments, the plurality of waveform characteristics may include a value based on at least one of a maximum value of the first section signal, a minimum value of the first section signal, a difference between the maximum and minimum values ​​of the first section signal, a standard deviation of the first section signal, a variance of the first section signal, an average value of the first section signal, a median value of the first section signal, and a value at an inflection point of the first section signal. By using these characteristics, it is possible to improve the accuracy of estimating the state of the rotating body.

[0021] In some embodiments, the processor may estimate the state of the rotating body using a machine learning model for estimating the state of the rotating body, in which case the accuracy of estimating the state of the rotating body can be improved by sufficiently training the machine learning model.

[0022] In some embodiments, the state of the rotating body may include at least one of a camber angle, a slip angle, a load applied to the rotating body, and an air pressure. The tendency of the change in the first sensor signal when the camber angle changes, the tendency of the change in the first sensor signal when the slip angle changes, the tendency of the change in the first sensor signal when the load changes, and the tendency of the change in the first sensor signal when the air pressure changes are different from one another. Therefore, the camber angle, the slip angle, the load, and the air pressure can be estimated separately.

[0023] In some embodiments, the first sensor and the processor may form a sensor module. The sensor module may be provided on the rotating body. The processor may output the estimation result to an external device provided outside the rotating body. In this case, the first sensor signal is processed within the sensor module, and the estimation result is output to the external device. Compared to a configuration in which the first sensor signal is processed in the external device, it is possible to reduce the amount of communication between the sensor module and the external device.

[0024] In some embodiments, the first sensor may be a piezoelectric element that generates electrical energy in response to a pressing force. The processor may operate using the electrical energy generated by the piezoelectric element. In this case, the processor can operate without receiving an external power supply. Therefore, wiring or the like for supplying power from an external source is not required, which simplifies the configuration of the estimation system.

[0025] In some embodiments, the first sensor may be a piezoelectric element that generates electrical energy in response to a pressing force. The processor may estimate the state of the rotating body by using the voltage or current of the electrical energy generated by the piezoelectric element as the first sensor signal. In this case, the state of the rotating body can be estimated with a simple configuration in which the piezoelectric element is disposed between the wheel and the tire.

[0026] [2] Example of embodiment Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated description will be omitted.

[0027] An estimation system according to one embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram schematically illustrating a vehicle equipped with an estimation system according to one embodiment. FIG. 2 is a perspective view of a rotating body shown in FIG. 1. FIG. 3 is a configuration diagram schematically illustrating the configuration of the estimation system shown in FIG. 1. FIG. 4 is an exploded perspective view of a sensor module shown in FIG. 1. The estimation system 1 shown in FIG. 1 is a system that estimates the state of a rotating body 2. The estimation system 1 can be mounted on, for example, a vehicle V. The vehicle V includes a rotating body 2 and is configured to be movable by rotation of the rotating body 2. Examples of the vehicle V may include automobiles, bicycles, and motorcycles. In this embodiment, an automobile will be used as an example of the vehicle V, but the technology according to the present disclosure is not limited to application to automobiles. The vehicle V includes four rotating bodies 2 provided at the front, rear, left, and right.

[0028] As shown in FIG. 2, the rotating body 2 is an element that can rotate around a rotation axis AX. The rotating body 2 has an outer end 2a (first end; see FIG. 14) and an inner end 2b (second end; see FIG. 14). The outer end 2a and the inner end 2b are opposite ends of the rotating body 2 in the direction in which the rotation axis AX extends (the direction of the rotation axis). The outer end 2a faces the outside of the vehicle V. The rotating body 2 includes a wheel 21 and a tire 22.

[0029] The wheel 21 is a component that transmits rotational force about the rotation axis AX to the tire 22. The wheel 21 may be made of a rigid component. Examples of materials that the wheel 21 may be made of include metal materials such as steel, magnesium, aluminum, and stainless steel, as well as resin materials such as carbon fiber. In the specific example shown in FIG. 2, the wheel 21 includes a rim 23 and a plurality of spokes 24. The rim 23 is an annular component that forms the outer edge of the wheel 21. The tire 22 is mounted along the outer periphery of the rim 23. Each of the plurality of spokes 24 extends radially from the center of the wheel 21 to the rim 23. The rim 23 and the spokes 24 may be integrally formed or may be separate components.

[0030] The tire 22 is an annular member mounted on the wheel 21. The tire 22 is provided along the outer periphery (rim 23) of the wheel 21. The tire 22 may be made of a flexible member. Examples of materials for the tire 22 may include resin such as rubber.

[0031] As shown in FIG. 3, the estimation system 1 includes a sensor module 3. The sensor module 3 is a module capable of detecting a pressing force acting on the rotating body 2. The sensor module 3 is provided on the rotating body 2. Specifically, the sensor module 3 is disposed between the wheel 21 (rim 23) and the tire 22. The sensor module 3 may be sandwiched between the wheel 21 (rim 23) and the tire 22 in the vertical direction, for example. In this embodiment, a plurality of sensor modules 3 are provided at equal intervals along the outer periphery of the wheel 21 (rim 23). Some sensor modules 3 are disposed at the outer end 2a (outer rim). The sensor module 3 may also be disposed at the inner end 2b (inner rim).

[0032] The number and positions of the sensor modules 3 provided on one rotating body 2 can be selected as appropriate. In this embodiment, multiple sensor modules 3 are provided on one rotating body 2. However, for example, one sensor module 3 may be provided on one rotating body 2. This configuration is not limited to this, and the number of sensor modules provided on one rotating body 2 may be, for example, two, three, four, five, six, seven, eight, nine, ten, or eleven or more. For example, the number of sensor modules 3 provided on one rotating body 2 may be the same as the number of spokes 24. For example, the number of sensor modules 3 provided on one rotating body 2 may be the same as the distance between two adjacent spokes 24. When multiple sensor modules 3 are provided on one rotating body 2, the sensor modules 3 may be arranged at equal intervals along the outer periphery of the wheel 21 (rim 23). As an alternative, the multiple sensor modules 3 may be arranged at different intervals along the outer periphery of the wheel 21 (rim 23). In yet another embodiment, at least some of the multiple sensor modules 3 may be arranged at equal intervals along the outer periphery of the wheel 21 (rim 23), and the other sensor modules 3 may be arranged at different intervals along the outer periphery of the wheel 21 (rim 23).

[0033] In the specific example shown in FIG. 4, each sensor module 3 is configured to be able to be arranged between the wheel 21 (rim 23) and the tire 22. Each sensor module 3 includes a piezoelectric element 31 (first sensor), a back plate 32, a substrate 33, a substrate 34, and a base material 35. The piezoelectric element 31 is an element that generates electric energy in response to an external force, such as a pressing force, acting on the piezoelectric element 31. An example of the piezoelectric element 31 may include a piezo ceramic element (piezo element). The piezoelectric element 31 may be formed in a plate shape.

[0034] The back plate 32 is a plate-like member that protects the piezoelectric element 31. The back plate 32 may be made of a metal member (e.g., stainless steel) or a resin member. The back plate 32 has, for example, a plate shape that is slightly larger than the piezoelectric element 31. The back plate 32 can also relieve stress on the piezoelectric element 31 by being placed on top of the piezoelectric element 31. The thickness of the back plate 32 adjusts the amount of deformation of the piezoelectric element 31 in response to the pressing force acting on the sensor module 3.

[0035] The substrates 33 and 34 are plate-like members that extract the electrical energy generated in the piezoelectric element 31 as a sensor signal (first sensor signal). Specifically, the substrates 33 and 34 may extract the voltage or current of the electrical energy generated in the piezoelectric element 31 as the sensor signal. In this embodiment, as an example, a case will be described in which a voltage is treated as the sensor signal. The substrates 33 and 34 may be flexible printed circuit boards (FPC). The substrate 33 may be configured to include, for example, a main body portion 33a and a wiring portion 33b. The main body portion 33a is a portion that forms a laminated structure described later. The wiring portion 33b is a portion that connects the sensor module 3 to an external circuit or the like. The substrate 34 includes a main body portion 34a and a wiring portion 34b. The main body portion 34a is a portion that forms a laminated structure described later. The wiring portion 34b is a portion that connects the sensor module 3 to an external circuit or the like. In this embodiment, the shape of the substrate 33 is substantially the same as the shape of the substrate 34, but the shape of the substrate 33 may be different from the shape of the substrate 34. The main body portions 33a and 34a may be formed to have substantially the same size as the back plate 32, for example.

[0036] The base material 35 is a member for attaching the sensor module 3 to the wheel 21. The base material 35 has a shape that follows the rim 23. The base material 35 is provided with a recess 35a that can accommodate a laminated structure, which will be described later.

[0037] In the specific example shown in FIG. 4 , the back plate 32 is superimposed on the piezoelectric element 31, and the superimposed piezoelectric element 31 and back plate 32 are sandwiched between the main body portion 33 a of the substrate 33 and the main body portion 34 a of the substrate 34. That is, the substrate 33, the back plate 32, the piezoelectric element 31, and the substrate 34 are stacked in this order to form a layered structure, and the layered structure is housed in the recess 35 a of the base material 35. In this manner, the sensor module 3 is formed. The sensor module 3 is disposed at a desired position between the rim 23 and the tire 22. In the specific example shown in FIG. 4 , the sensor module 3 may be disposed on the rotating body 2 so that the surface of the base material 35 opposite the surface on which the recess 35 a is provided contacts the rim 23. In this case, the surface of the main body portion 33 a of the substrate 33 opposite the back plate 32 contacts the tire 22.

[0038] Each sensor module 3 includes, for example, a piezoelectric element 31 as a circuit element. Each sensor module 3 may include, for example, an analog-to-digital (AD) converter 41, a processor 42, a communication interface 43, a power converter 44, and a power storage device 45 in addition to the piezoelectric element 31. The AD converter 41, the processor 42, the communication interface 43, the power converter 44, and the power storage device 45 may be mounted on the substrate 33 or the substrate 34.

[0039] The AD converter 41 is a circuit element that converts the analog sensor signal output from the piezoelectric element 31 into a digital sensor signal. The AD converter 41 outputs the digital sensor signal to the processor .

[0040] The processor 42 is a circuit element that estimates the state of the rotating body 2 based on sensor signals. The state of the rotating body 2 estimated by the processor 42 includes at least one of a camber angle, a slip angle, a load applied to the rotating body 2, and an air pressure. The processor 42 may output the estimation result to the external device 5 via the communication interface 43. Details of the processing performed by the processor 42 will be described later. Examples of the processor 42 include, but are not limited to, a central processing unit (CPU), a digital signal processor (DSP), an auxiliary support processor (ASP), a microcomputer, a programmable logic controller (PLC), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and an integrated circuit (IC). The processor 42 may have a multi-core configuration.

[0041] The communication interface 43 is hardware that enables the sensor module 3 to transmit and receive data to and from the external device 5 via the communication network NW1. The communication network NW1 may be configured as a wired communication network, a wireless communication network, or a combination thereof. Examples of the communication network NW1 may include one or more of the Internet, an intranet, a wide area network (WAN), a local area network (LAN), Bluetooth (registered trademark), a wireless LAN (Wi-Fi, etc.), a controller area network (CAN), and a mobile communication network. The communication interface 43 may, for example, comply with a specific communication protocol.

[0042] The power converter 44 is a device that converts the sensor signal (voltage) generated by the piezoelectric element 31 into a voltage that can be charged to the power storage device 45. The power converter 44 is, for example, a power conditioner. As will be described later, when the sensor signal includes a periodically changing AC signal, the power converter 44 may include a rectifier circuit.

[0043] The power storage device 45 is a chargeable and dischargeable device. The power storage device 45 stores the sensor signal generated by the piezoelectric element 31 as electrical energy (power) and supplies the electrical energy to circuit elements in the sensor module 3. For example, the processor 42 operates using the electrical energy generated by the piezoelectric element 31. Examples of the power storage device 45 may include a storage battery such as a lithium-ion battery, and a capacitor.

[0044] The external device 5 is a device capable of communicating with the sensor module 3. The external device 5 may be configured, for example, to present an estimation result regarding the state of the rotating body 2 to a person (passenger) riding in the vehicle V. The external device 5 may be configured, for example, to provide an estimation result regarding the state of the rotating body 2 to another device included in the vehicle V. The external device 5 may be configured, for example, to provide an estimation result regarding the state of the rotating body 2 to a device located outside the vehicle V (for example, a server connectable via a communication line).

[0045] The external device 5 may be provided outside the rotating body 2 and disposed within the vehicle V. Examples of the external device 5 may include an in-vehicle device and a mobile terminal carried by a passenger. Examples of the mobile terminal may include a smartphone, a tablet terminal, a laptop computer, etc. The external device 5 may include, for example, a processor 51, a memory 52, and a communication interface 55. The external device 5 may further include, for example, an input device 53, an output device 54, and a communication interface 56.

[0046] The processor 51 is a circuit element that performs control and calculations in the external device 5. The processor 51 is configured similarly to the processor 42. Examples of the processor 51 include, but are not limited to, a CPU, a DSP, an ASP, a microcomputer, a PLC, an FPGA, an ASIC, and an IC. The processor 51 may have a multi-core configuration. The memory 52 may include a main memory device and an auxiliary memory device. The main memory device is configured with a random access memory (RAM), a read-only memory (ROM), and the like. Examples of the auxiliary memory device include a semiconductor memory and a hard disk drive.

[0047] The input device 53 is a device that accepts input from a user of the external device 5. Examples of the input device 53 may include a touch panel, a keyboard, and a mouse. The output device 54 is a device that outputs information to the outside of the external device 5. Examples of the output device 54 may include a display and a speaker.

[0048] The communication interface 55 is hardware that enables the external device 5 to transmit and receive data to and from the sensor module 3 via the communication network NW1. The communication interface 55 may, for example, comply with a specific communication protocol. The communication interface 56 is hardware that enables the external device 5 to transmit and receive data to and from a device located outside the vehicle V (e.g., a server (not shown) connectable via the communication network NW2) via the communication network NW2. The communication network NW2 may be configured using wired communication, wireless communication, or a combination thereof. Examples of the communication network NW2 may include one or more of the Internet, an intranet, a WAN, a LAN, Bluetooth (registered trademark), Wi-Fi, a mobile communication network, and the like. The communication interface 56 may, for example, comply with a specific communication protocol.

[0049] The processor 51, memory 52, input device 53, output device 54, communication interface 55, and communication interface 56 may be communicatively connected to each other by, for example, a bus 57.

[0050] Next, the sensor signals will be described in detail with reference to Fig. 5 to Fig. 8. Fig. 5 is a diagram illustrating forces acting on the sensor module shown in Fig. 1. Fig. 6 is a diagram illustrating a sensor signal output from the sensor shown in Fig. 1. Fig. 7 is a diagram illustrating an example of a sensor signal when traveling at a constant speed. Fig. 8 is a diagram illustrating an example of a sensor signal when traveling at an accelerated speed.

[0051] In the specific example shown in FIG. 5 , the sensor module 3 is disposed between the outer flange of the rim 23 and the bead of the tire 22, and is in contact with the flange of the rim 23 and the bead of the tire 22. The weight W of the vehicle V acts as a pressing force on the piezoelectric element 31 via the wheel 21 (rim 23), and a reaction force R from the road surface acts as a pressing force via the tire 22. The piezoelectric element 31 outputs a sensor signal corresponding to the pressing force exerted by the wheel 21 and the tire 22. Specifically, the magnitude of the sensor signal varies depending on, for example, the magnitude of the pressing force acting on the piezoelectric element 31 and the amount of change in the pressing force per unit time. Note that, in this embodiment, the sensor module 3 is configured to output a negative sensor signal when the piezoelectric element 31 receives a pressing force; however, it may also be configured to output a positive sensor signal when a pressing force is received. As the pressing force acting on the piezoelectric element 31 increases, the absolute value of the sensor signal increases.

[0052] Specifically, during one rotation of the rotating body 2, the portion of the rotating body 2 (the outer peripheral surface of the tire 22) that comes into contact with the road surface changes, causing a change in the relative positional relationship between the piezoelectric element 31 and the road surface. For example, as the piezoelectric element 31 approaches the road surface, the weight W of the vehicle V acting on the piezoelectric element 31 via the wheel 21 (rim 23) increases, and the reaction force R from the road surface acting on the piezoelectric element 31 via the tire 22 becomes the largest. When the piezoelectric element 31 is closest to the road surface, the weight W of the vehicle V acting on the piezoelectric element 31 via the wheel 21 (rim 23) becomes the largest, and the reaction force R from the road surface acting on the piezoelectric element 31 via the tire 22 becomes the largest. At this time, the portion of the tire 22 located between the rim 23 and the road surface is compressed and elastically deformed. As the rotating body 2 rotates further, the weight W of the vehicle V acting on the piezoelectric element 31 via the wheel 21 (rim 23) decreases, and the reaction force R from the road surface acting on the piezoelectric element 31 via the tire 22 also decreases. Then, the compressed tire 22 returns to its original shape. At this time, elastic vibrations may occur in the tire 22, and in this case, the stress acting on the piezoelectric element 31 is attenuated while vibrating.

[0053] In the specific example shown in FIG. 6, while the rotating body 2 makes one rotation, the sensor signal has a steep peak that is convex in the negative direction, followed by a steep peak that is convex in the positive direction. The sensor signal then oscillates and attenuates. When the vehicle V is traveling at a constant speed, the rotational speed of the rotating body 2 is approximately constant. Therefore, as shown in FIG. 7, the waveform for one rotation is repeated at a constant period. When the vehicle V is accelerating, the rotational speed of the rotating body 2 gradually increases. Therefore, as shown in FIG. 8, the period of the waveform for one rotation becomes shorter. When accelerating, the reaction force from the road surface may increase, in which case the absolute value of the negative peak gradually increases.

[0054] Next, an estimation method performed by the processor 42 will be described with reference to Fig. 9. Fig. 9 is a flowchart showing the estimation method performed by the processor shown in Fig. 1. The processor 42 may perform the estimation method by, for example, reading out an estimation program stored in a computer-readable non-transitory recording medium and executing the estimation program. Note that such a recording medium may include, for example, a ROM or the like accessible by the processor 42. The series of processes shown in Fig. 9 is started, for example, every time a certain time period has elapsed.

[0055] First, the processor 42 acquires a sensor signal from the piezoelectric element 31 (step S1). Specifically, the processor 42 may acquire the sensor signal converted into a digital signal by the AD converter 41, for example.

[0056] Next, processor 42 generates a section signal by dividing the sensor signal into specific sections (step S2). Below, several examples of the process for generating a section signal will be described with reference to FIGS. 10 to 13, but the process for generating a section signal is not limited to these examples. FIGS. 10 to 13 are diagrams for explaining an example of the process for generating a section signal. The horizontal axis in FIGS. 10 to 13 indicates time. The vertical axis in FIG. 10 indicates voltage. The vertical axis in FIGS. 11 to 13 indicates normalized output. The normalized output represents a value obtained by dividing the voltage value of the sensor signal by a predetermined voltage value. Note that the sensor signal may contain noise components. Therefore, processor 42 may remove the noise components from the sensor signal and generate the section signal using the sensor signal from which the noise components have been removed.

[0057] As shown in FIG. 10 , the processor 42 may divide the sensor signal into specific interval signals using window control. Specifically, the processor 42 may use a window having a time width and select a portion of the sensor signal included in the window as the interval signal. The time width of the window may be a predetermined fixed value or a variable set value. The time width of the window is, for example, about 5 seconds. The time width of the window is not limited to this and may be greater than or equal to 1 second, less than 5 seconds, or even greater than 5 seconds. The processor 42 shifts the window by a certain time and selects a portion of the sensor signal included in the shifted window as the next interval signal. The time for shifting the window (shift time) may be, for example, about 1 second. The shift time is not limited to this and may be less than the time width of the window. Similarly, the processor 42 selects an interval signal each time the window is shifted. According to this technique, for example, by using a fixed window, the processing load of the processor 42 can be reduced.

[0058] The time width of the window may be dynamically set. For example, the processor 42 may identify the fundamental period of the sensor signal using a fast Fourier transform (FFT) and set the fundamental period as the time width of the window.

[0059] As another method, as shown in FIG. 11 , the processor 42 may select the section signal using the maximum and minimum values ​​included in the sensor signal. Specifically, the processor 42 may, for example, identify a peak in a section of the sensor signal that exceeds a threshold for determining a maximum value as the maximum value. The processor 42 may, for example, identify a peak (bottom) in a section of the sensor signal that is below a threshold for determining a minimum value as the minimum value. The threshold for determining a maximum value and the threshold for determining a minimum value may be set in advance. Note that, if maximum and minimum values ​​alternate in the sensor signal, the processor 42 may identify the maximum and minimum values ​​using this fact as a constraint. In this case, the processor 42 may set a window to include one consecutive maximum and one consecutive minimum value, and select a portion of the sensor signal included in the window as the section signal.

[0060] When the rotating body 2 rotates while in contact with the road surface, in certain circumstances, a minimum value of the sensor signal appears when the piezoelectric element 31 is closest to the road surface, and a maximum value of the sensor signal appears when the piezoelectric element 31 moves away from the road surface (when the pressing force acting on the piezoelectric element 31 is released). In this case, a section including one consecutive maximum value and one consecutive minimum value can correspond to the sensor signal for one rotation of the rotating body 2. From the above, according to this method, even if the rotational speed of the rotating body 2 changes, the sensor signal for one rotation of the rotating body 2 can be selected as the section signal. In this case, according to this method, it is possible to select a section for one rotation of the rotating body 2 as the above-mentioned specific section, and the processor 42 can generate the section signal by dividing the sensor signal by the section for one rotation of the rotating body 2.

[0061] As yet another method, as shown in Fig. 12, the processor 42 may select the section signal using zero-crossing points included in the sensor signal. Specifically, the processor 42 identifies, for example, zero-crossing points in the sensor signal where the sensor signal changes from a negative value to a positive value. Then, the processor 42 sets a window between two consecutive zero-crossing points and selects a portion of the sensor signal included in the window as the section signal.

[0062] When the rotating body 2 rotates while in contact with the road surface, in some circumstances, the sensor signal changes abruptly from a minimum value to a maximum value between when the piezoelectric element 31 approaches the road surface closest to the road surface and when it moves away from the road surface. In this case, the zero-crossing point where the sensor signal changes from a negative value to a positive value occurs when the piezoelectric element 31 approaches the road surface closest to the road surface and when it moves away from the road surface. Therefore, the section defined by two consecutive zero-crossing points can correspond to the sensor signal for one rotation of the rotating body 2. From the above, according to this method, even if the rotational speed of the rotating body 2 changes, the sensor signal for one rotation of the rotating body 2 can be selected as the section signal. In this case, according to this method, the section for one rotation of the rotating body 2 can be selected as the specific section, and the processor 42 can generate the section signal by dividing the sensor signal by the section for one rotation of the rotating body 2.

[0063] The sensor signal may change from a negative value to a positive value at times other than when the piezoelectric element 31 moves away from the road surface after coming closest to the road surface. In this case, the processor 42 may specify the zero-crossing point by further using a condition that the amount of change (rate of change) of the sensor signal per unit time is greater than a predetermined value.

[0064] 13, the processor 42 may select the section signal using an acceleration signal output from an acceleration sensor provided on the wheel 21. The acceleration sensor may be disposed, for example, at the center of the wheel 21. Specifically, the processor 42 sets one period of the acceleration signal as a window, and selects a portion of the sensor signal that is included in the window as the section signal.

[0065] As the rotating body 2 rotates, the direction of the gravitational acceleration detected by the acceleration sensor changes, and the acceleration signal has a periodic waveform. For example, if the rotational speed of the rotating body 2 is constant, the acceleration signal will be a sine wave. In this case, one period of the acceleration signal corresponds to one rotation of the rotating body 2. As described above, according to this method, even if the rotational speed of the rotating body 2 changes, the sensor signal for one rotation of the rotating body 2 can be selected as the section signal. In this case, according to this method, a section for one rotation of the rotating body 2 can be selected as the above-mentioned specific section, and the processor 42 can generate the section signal by dividing the sensor signal by the section for one rotation of the rotating body 2.

[0066] The acceleration signal may contain noise components, so processor 42 may remove the noise components from the acceleration signal and use the noise-removed acceleration signal to perform the technique shown in Figure 13.

[0067] Next, the processor 42 estimates the state of the rotating body 2 based on the section signal (step S3). As described above, the state of the rotating body 2 estimated by the processor 42 includes, for example, at least one of the camber angle, slip angle, load applied to the rotating body 2, and air pressure. In other words, the parameters representing the state of the rotating body 2 may include the camber angle, slip angle, load, and air pressure. When each parameter changes, the waveform of the sensor signal changes. The degree of influence of each parameter on the waveform of the sensor signal may differ from one another.

[0068] The influence of each parameter on the waveform of the sensor signal will be described below with reference to FIGS. 14 to 23. FIG. 14 is a diagram illustrating the reaction force from the road surface when the camber angle is 0 degrees. FIG. 15 is a diagram illustrating the reaction force from the road surface when the camber angle is positive. FIG. 16 is a diagram illustrating the reaction force from the road surface when the camber angle is negative. FIG. 17 is a diagram illustrating an example of the sensor signal for each camber angle. FIG. 18 is a diagram illustrating the slip angle. FIG. 19 is a diagram illustrating the force acting on the sensor module when a slip angle is occurring. FIG. 20 is a diagram illustrating an example of the sensor signal for each slip angle. FIG. 21 is a diagram illustrating the peak-to-peak value and the second peak value. FIG. 22 is a diagram illustrating the relationship between the peak-to-peak value and the damping rate when the slip angle, camber angle, load, and air pressure are changed. FIG. 23 is a partially enlarged view of FIG. 22.

[0069] As shown in FIGS. 14 to 16, when the camber angle θ changes, the reaction force that the rotating body 2 receives from the road surface RS changes. The camber angle θ can be expressed, for example, as the inclination angle of the rotating body 2 when the vehicle V is viewed from the front. Note that the camber angle θ may also be expressed, for example, as the inclination of the rotating body 2 with respect to the road surface RS. In the specific example shown in FIGS. 14 to 16, the camber angle θ is expressed as the angle between the central axis CX1 of the rotating body 2 and the normal direction to the road surface RS. The central axis CX1 is the vertical axis of the rotating body 2. When the upper end of the rotating body 2 is tilted outward, the camber angle θ is a positive value (positive). This state can be expressed as the upper end of the rotating body 2 being tilted in the positive direction (positive camber). When the upper end of the rotating body 2 is tilted inward, the camber angle θ is a negative value (negative). This state can be expressed as the upper end of the rotating body 2 being tilted in the negative direction (negative camber). In the specific examples shown in FIGS. 14 to 16, the upper end of the rotating body 2 represents the end opposite to the road surface RS.

[0070] As shown in Fig. 14, when the camber angle θ is 0 degrees, a uniform reaction force from the road surface RS acts on the portion of the rotating body 2 (tire 22) that comes into contact with the road surface RS. As shown in Fig. 15, when the camber angle θ is positive, the reaction force from the road surface RS increases toward the outer end 2a of the rotating body 2. As shown in Fig. 16, when the camber angle θ is negative, the reaction force from the road surface RS increases toward the inner end 2b of the rotating body 2.

[0071] As an example of this embodiment, a case will be described in which the sensor module 3 is disposed at the outer end 2a (outer rim). In this case, as shown in FIG. 17, as the camber angle θ increases, the reaction force that the piezoelectric element 31 receives from the road surface RS increases. Therefore, as the camber angle θ increases, the peak-to-peak value of the sensor signal increases. The peak-to-peak value may be expressed, for example, as the absolute value of the difference between the minimum value in the negative direction and the maximum value in the positive direction in FIG. 17. Furthermore, due to the reaction force received from the road surface RS, the bead of the tire 22 approaches the flange of the rim 23, and the piezoelectric element 31 is pressed against the bead of the tire 22 and the flange of the rim 23. Therefore, the degree of freedom of the piezoelectric element 31 decreases. Note that in this embodiment, the degree of freedom of the piezoelectric element 31 may represent, for example, the degree to which the piezoelectric element 31 can deform. As a result, as the camber angle θ increases, the vibration after the peak of the sensor signal tends to decrease.

[0072] On the other hand, as the camber angle θ decreases, the reaction force that the piezoelectric element 31 receives from the road surface RS decreases. As a result, as the camber angle θ decreases, the peak-to-peak value of the sensor signal decreases. Furthermore, the force that the bead of the tire 22 and the flange of the rim 23 apply to the piezoelectric element 31 weakens, increasing the degree of freedom of the piezoelectric element 31. As a result, as the camber angle θ decreases, the vibration after the peak of the sensor signal tends to increase.

[0073] As shown in FIG. 18, the slip angle φ is the angle of inclination of the rotor 2 when the vehicle V is viewed from above (for example, when looking down on the vehicle V or the rotor 2 that is on the road surface). Specifically, the slip angle φ is the angle formed between the orientation CX2 of the rotor 2 and the traveling direction F of the vehicle V. The orientation CX2 of the rotor 2 may be, for example, perpendicular to the direction in which the rotation axis AX of the rotor 2 extends and substantially parallel to the road surface. For the sake of explanation below, the slip angle φ is expressed as a positive value when the front end of the rotor 2 is inclined toward the outside of the vehicle V with respect to the traveling direction F. The slip angle φ is expressed as a negative value when the front end of the rotor 2 is inclined toward the inside of the vehicle V with respect to the traveling direction F. Note that FIG. 18 shows the rotor 2 on the right side of the vehicle V. For this rotor 2, the right direction with respect to the traveling direction F is the outside of the vehicle V, and the left direction with respect to the traveling direction F is the inside of the vehicle V. For the rotating body 2 on the left side of the vehicle V, the left direction relative to the traveling direction F is the outside of the vehicle V, and the right direction relative to the traveling direction F is the inside of the vehicle V.

[0074] As shown in FIG. 19, as the slip angle φ changes, the degree of freedom of the piezoelectric element 31 changes. When the slip angle φ is a positive value, the force that moves the bead of the tire 22 closer to the flange of the rim 23 increases toward the outer end 2a of the rotating body 2. In this case, for example, the pressing force between the tire 22 and the rim 23 at the outer end 2a (outer rim side) of the rotating body 2 is greater than the pressing force between the tire 22 and the rim 23 at the inner end 2b (inner rim side) of the rotating body 2. When the sensor module 3 is disposed at the outer end 2a (outer rim), the piezoelectric element 31 is pressed by the bead of the tire 22, reducing the degree of freedom of the piezoelectric element 31. Therefore, as shown in FIG. 20 (particularly when the slip angle is positive in FIG. 20), vibration after the peak of the sensor signal is suppressed.

[0075] On the other hand, when the slip angle φ is a negative value, the bead of the tire 22 receives a force that pulls it away from the flange of the rim 23 as it moves toward the outer end 2a of the rotating body 2. In this case, for example, the pressing force between the tire 22 and the rim 23 at the outer end 2a (outer rim side) of the rotating body 2 is smaller than the pressing force between the tire 22 and the rim 23 at the inner end 2b (inner rim side) of the rotating body 2. Therefore, the force with which the bead of the tire 22 presses the piezoelectric element 31 is alleviated, increasing the degree of freedom of the piezoelectric element 31. Therefore, as shown in FIG. 20, the vibration after the peak of the sensor signal becomes larger.

[0076] Even if the slip angle φ changes, the reaction force from the road surface acting on the piezoelectric element 31 may not change much. On the other hand, the larger the slip angle φ, the stronger the force with which the bead of the tire 22 presses down on the piezoelectric element 31. For this reason, in some cases, the peak-to-peak value of the sensor signal may increase slightly as the slip angle φ increases.

[0077] When the load changes, the force that the piezoelectric element 31 receives from the vehicle body changes. Specifically, as the load increases, the force that the rotating body 2 receives from the vehicle body increases. At this time, the pressing force applied to the sensor module 3 increases, and the peak-to-peak value of the sensor signal increases. On the other hand, as the load decreases, the force that the rotating body 2 receives from the vehicle body decreases. At this time, the pressing force applied to the sensor module 3 decreases, and the peak-to-peak value of the sensor signal decreases. In other words, as the voltage generated by the piezoelectric element 31 changes due to a change in load, the waveform of the sensor signal expands and contracts in the vertical axis direction (voltage value).

[0078] When the air pressure changes, the elastic modulus of the tire 22 changes. The higher the air pressure, the less the tire 22 compresses, and therefore the smaller the reaction force acting from the road surface on the piezoelectric element 31. This reduces the peak-to-peak value of the sensor signal. On the other hand, the lower the air pressure, the more the tire 22 compresses, and therefore the greater the reaction force acting from the road surface on the piezoelectric element 31. This increases the peak-to-peak value of the sensor signal. In other words, the voltage generated by the piezoelectric element 31 changes in response to changes in air pressure, and therefore the waveform of the sensor signal expands and contracts in the vertical axis direction.

[0079] The processor 42 estimates the state of the rotating body 2 based on the degree of influence of each parameter on the waveform of the sensor signal. Below, several examples of the state estimation process for the rotating body 2 will be described, but the state estimation process for the rotating body 2 is not limited to these examples.

[0080] As one method, the processor 42 may estimate the state of the rotating body 2 based on a plurality of different waveform characteristics calculated from the section signal. The plurality of waveform characteristics include a value based on at least one of the maximum value of the section signal, the minimum value of the section signal, the difference between the maximum and minimum values ​​of the section signal (peak-to-peak value), the standard deviation of the section signal, the variance of the section signal, the average value of the section signal, the median value of the section signal, the value at an inflection point of the section signal, and the wavelength of the section signal. For example, as the plurality of waveform characteristics, one or more of the values ​​exemplified above may be used as is, or a combination of two or more values ​​may be used, or a value calculated from these values ​​using an appropriate formula may be used.

[0081] For each parameter (camber angle, slip angle, load, and air pressure) representing the state of the rotating body 2, the relationship between the amount of change in that parameter and the amount of change in each waveform characteristic may be measured and stored in advance. Specifically, for each parameter representing the state of the rotating body 2, the relationship between the amount of change in that parameter when only that parameter changes and the amount of change in each waveform characteristic may be stored. Here, the number of waveform characteristics used in the state estimation process may be equal to or greater than the number of parameters to be estimated among the parameters representing the state of the rotating body 2.

[0082] As an example, changes in the peak-to-peak value and the attenuation rate in response to changes in each parameter will be described. The attenuation rate is the attenuation rate of the waveform of the sensor signal generated when the piezoelectric element 31 moves away from the road surface. The attenuation rate is a value obtained by dividing the second peak value by the peak-to-peak value. As shown in FIG. 21, for example, the positively convex peak value of the voltage generated after the maximum value in the section signal may be used as the second peak value. If the section signal does not have any positively convex peak values ​​other than the maximum value, for example, the value at the inflection point where the rate of change of the slope of the section signal switches from positive to negative after the maximum value may be used as the second peak value.

[0083] 22 and 23, the state of the rotating body 2 when the camber angle is 0 degrees, the slip angle is 0 degrees, the load is 5300 N, and the air pressure is 240 kPa is used as the reference state. The reference state represents the state of the rotating body 2 at a specific speed, a specific camber angle, a specific slip angle, a specific load, and a specific air pressure. In the reference state, the peak-to-peak value is 2.9 V, and the damping ratio is 0.042.

[0084] In the examples shown in Figures 22 and 23, as the camber angle increases, the peak-to-peak value increases and the damping ratio decreases. Specifically, when the camber angle alone is changed from -5 degrees to +5 degrees from the reference state, the peak-to-peak value increases from 1.6 V to 3.7 V, and the damping ratio decreases from 0.077 to 0.030. As the slip angle increases, the peak-to-peak value increases and the damping ratio decreases. Specifically, when the slip angle alone is changed from -1 degree to +1 degree from the reference state, the peak-to-peak value increases from 2.6 V to 3.4 V, and the damping ratio decreases from 0.200 to -0.460.

[0085] In the examples shown in Figures 22 and 23, as the load increases, the peak-to-peak value increases and the damping rate increases. Specifically, when the load alone is changed from 3000 N to 7600 N from the reference state, the peak-to-peak value increases from 1.8 V to 3.8 V, and the damping rate increases from 0.037 to 0.052. As the air pressure increases, the peak-to-peak value decreases and the damping rate decreases. Specifically, when the air pressure alone is changed from 160 kPaN to 260 kPaN, the peak-to-peak value decreases from 2.9 V to 2.6 V, and the damping rate decreases from 0.100 to 0.083.

[0086] The processor 42 may estimate the state of the rotating body 2 by comparing the actual measurement value with a reference value. The reference value is the value of each waveform characteristic in the reference state of the rotating body 2. The actual measurement value is the value of each waveform characteristic obtained from the section signal. Specifically, if the actual measurement value of any waveform characteristic differs from the reference value, the processor 42 determines that the state of the rotating body 2 has changed from the reference state. The processor 42 may then calculate the value of the parameter to be estimated based on the amount of change in each waveform characteristic. As an example, the processor 42 may estimate the state of the rotating body 2 using the relationships shown in FIGS. 22 and 23. In this case, the processor 42 may, for example, target two parameters of the state of the rotating body 2 as estimation targets, and calculate the values ​​of the two parameters to be estimated from the actual measurement values, assuming that the parameters other than the target parameters have not changed.

[0087] The processor 42 may assume that one of the multiple parameters has changed, and estimate which parameter has changed from the amount of change in each waveform characteristic (a value obtained by subtracting a reference value from an actual measurement value).

[0088] As another method, the processor 42 may determine the state of the rotating body 2 using a clustering method such as the k-means method. Specifically, the processor 42 classifies the section signal into one of the clusters set in accordance with each parameter of the rotating body 2, based on the actual measurement values ​​of each waveform characteristic obtained from the section signal. The processor 42 estimates, as the state of the rotating body 2, the state corresponding to the cluster into which the section signal has been classified.

[0089] As yet another method, the processor 42 may estimate the state of the rotating body 2 using an estimation model M. The estimation model M may be, for example, a machine learning model trained to estimate the state of the rotating body 2. The estimation model M will be described with reference to FIG. 24. FIG. 24 is a diagram for explaining the estimation model. As shown in FIG. 24, the estimation model M may be generated, for example, by machine learning using training data. Algorithms such as random forest, LightGBM, and deep learning may be used as the machine learning algorithm. Note that the estimation model M may be, for example, a classifier that classifies the state of the rotating body 2 into specific categories (for example, a camber angle range, a slip angle range, a load range, etc.), or may be a regression model that outputs an estimated value of the state of the rotating body 2.

[0090] The training data may include, for example, a feature vector calculated from a section signal generated from a sensor signal acquired in advance by the sensor module 3. The feature vector may include, as elements, values ​​of a plurality of waveform characteristics. The feature vector may include, as elements, one or more of the following: the maximum value of the section signal, the minimum value of the section signal, the peak-to-peak value of the section signal, the standard deviation of the section signal, the variance of the section signal, the average value of the section signal, the median value of the section signal, a value at an inflection point of the section signal (e.g., the second peak value), the wavelength of the section signal, and a value calculated from these values. Without being limited thereto, the feature vector may be, for example, all data included in the section signal (e.g., the voltage value itself). The training data may be assigned a label according to the state of the rotating body 2. Examples of labels may include normal driving, a change in camber angle, and a change in slip angle. A change in a parameter may be used as a label. For example, a camber angle range, a slip angle range, a load range, an air pressure range, etc. may be used as a label.

[0091] The estimation model M receives as input the feature vector calculated from the section signal and outputs an estimation result. The estimation result is information indicating the state of the rotating body 2. The estimation result may include information indicating which parameters have changed. The estimation result may include the amount of change in each parameter. The estimation result may include the range of each parameter (e.g., the range of camber angle, the range of slip angle, the range of load, the range of air pressure, etc.).

[0092] 24, the estimation model M is configured to estimate all states using one model. However, the estimation model M may include multiple estimation models provided for each parameter to be estimated (e.g., camber angle, slip angle, load, air pressure, etc.). Each estimation model estimates a state assigned to the estimation model.

[0093] Next, the processor 42 outputs the estimation result (step S4). In the present embodiment, the processor 42 may output the estimation result to the external device 5, for example, via the communication interface 43. Upon receiving the estimation result, the external device 5 may present the estimation result to the occupant, for example, using the output device 54. For example, if the output device 54 is a display, the output device 54 displays the estimation result. Without being limited to this, the external device 5 may, for example, provide the received estimation result to another device installed in the vehicle V. For example, the external device 5 may provide the received estimation result to a device located outside the vehicle V (for example, a server connectable via the communication network NW2).

[0094] This completes the series of processes in the estimation method.

[0095] In the estimation system 1, estimation method, and estimation program described above, a sensor signal corresponding to the pressing force exerted by the wheel 21 and the tire 22 is output from the piezoelectric element 31 disposed between the wheel 21 and the tire 22. The weight W of the vehicle V (vehicle body) acts on the piezoelectric element 31 via the wheel 21, and a reaction force R from the road surface acts on the piezoelectric element 31 via the tire 22. These forces can change depending on the state of the rotating body 2, so the state of the rotating body 2 can be estimated based on the sensor signal. Therefore, the state of the rotating body 2 can be estimated with a simple configuration in which the piezoelectric element 31 (sensor module 3) is disposed between the wheel 21 and the tire 22.

[0096] When the wheel 21 includes a rim 23, the tire 22 is mounted on the rim 23. In this case, the piezoelectric element 31 is disposed between the rim 23 and the tire 22. Therefore, with a simple configuration in which the piezoelectric element 31 (sensor module 3) is disposed between the rim 23 and the tire 22, it is possible to estimate the state of the rotating body 2.

[0097] If the piezoelectric element 31 is disposed at the center of the rotating body 2 in the direction of extension of the rotation axis AX, the sensor signal changes in the same manner regardless of whether the camber angle changes in the positive or negative direction. On the other hand, in the above-described embodiment, if the piezoelectric element 31 is disposed at the outer end 2a, the sensor signal changes asymmetrically with respect to changes in the camber angle, etc. Here, "the sensor signal changes asymmetrically" means that the sensor signal differs when the camber angle changes in the positive direction and when the camber angle changes in the negative direction. For example, when the camber angle increases in the positive direction, the reaction force from the road surface increases toward the outer end 2a of the rotating body 2, and therefore the peak-to-peak value of the sensor signal increases. For example, when the camber angle decreases, the reaction force from the road surface increases toward the inner end 2b of the rotating body 2, and therefore the peak-to-peak value of the sensor signal decreases. In other words, by disposing the piezoelectric element 31 at the outer end 2a of the rotating body 2, it is possible to improve the accuracy of estimating the state of the rotating body 2.

[0098] On the other hand, even if the piezoelectric element 31 is arranged at the inner end 2b, the sensor signal changes asymmetrically with respect to changes in the camber angle, etc. In this case, the reaction force from the road surface at the inner end 2b of the rotating body 2 changes depending on the camber angle. Therefore, even in a configuration in which the piezoelectric element 31 is arranged at the inner end 2b, it is possible to improve the accuracy of estimating the state of the rotating body 2.

[0099] As described above, the section signal may be generated, for example, by dividing the section into sections corresponding to one rotation of the rotating body 2. As the rotating body 2 rotates, the portion of the rotating body 2 that comes into contact with the road surface changes, and the relative positional relationship between the piezoelectric element 31 and the contact portion changes. For this reason, in certain situations, the sensor signal has a periodicity in which the waveform shape becomes similar every time the rotating body 2 rotates once. In this case, it is possible to estimate the state of the rotating body 2 by analyzing the section signal corresponding to one rotation of the rotating body 2.

[0100] The waveform characteristics calculated from the section signals can be an index representing the state of the rotating body 2. Therefore, by using a plurality of different waveform characteristics calculated from the section signals, it is possible to improve the accuracy of estimating the state of the rotating body 2.

[0101] The maximum value of the section signal, the minimum value of the section signal, the peak-to-peak value of the section signal, the standard deviation of the section signal, the variance of the section signal, the average value of the section signal, the median value of the section signal, and the value at the inflection point of the section signal are values ​​that represent the waveform characteristics of the section signal. If the state of the rotating body 2 changes, these values ​​may change. Therefore, by using a value based on at least one of these values, it is possible to improve the accuracy of estimating the state of the rotating body 2.

[0102] The processor 42 may estimate the state of the rotating body 2 using the estimation model M. In this case, by allowing the estimation model M to learn sufficiently, it is possible to improve the accuracy of estimating the state of the rotating body 2.

[0103] As described above, the trends of the changes in the sensor signal when the camber angle, slip angle, load, and air pressure change may be different from one another. In this case, the camber angle, slip angle, load, and air pressure can be estimated separately.

[0104] As described above, the piezoelectric element 31 generates electrical energy in response to the pressing force. For example, the processor 42 may be configured to operate using the electrical energy generated by the piezoelectric element 31. With this configuration, the processor 42 can operate without receiving a supply of power from outside the sensor module 3. Therefore, wiring or the like for supplying power from outside the sensor module 3 is not required, and the configuration of the estimation system 1 can be simplified.

[0105] As described above, the piezoelectric element 31 and the processor 42 may constitute the sensor module 3. Such a sensor module 3 may be provided on the rotating body 2. The processor 42 may be configured to output the estimation result to an external device 5 provided outside the rotating body 2. In this configuration, the sensor signal is processed within the sensor module 3, and the estimation result is output to the external device 5. In this case, the amount of communication between the sensor module 3 and the external device 5 can be reduced compared to a configuration in which the sensor signal is processed in the external device 5. This can reduce the power required for communication, making it possible to effectively utilize the electrical energy generated by the piezoelectric element 31.

[0106] Next, an estimation system according to another embodiment will be described with reference to Fig. 25. Fig. 25 is a schematic diagram of an estimation system according to another embodiment. The estimation system 1A shown in Fig. 25 differs from the estimation system 1 mainly in that, instead of the single sensor module 3, the estimation system 1A includes multiple sensor modules 3A and one control module 4.

[0107] Each sensor module 3A differs from the sensor module 3 mainly in that it does not include an AD converter 41, a processor 42, a communication interface 43, a power converter 44, and a power storage device 45 as circuit elements.

[0108] Each sensor module 3A may be configured to have the same physical structure as the sensor module 3, for example, and may include a piezoelectric element 31, a back plate 32, a substrate 33, a substrate 34, and a base material 35. Multiple sensor modules 3A may be provided on the same rotating body 2, for example. Each sensor module 3A is disposed between the wheel 21 (rim 23) and the tire 22. Specifically, each sensor module 3A is disposed between the flange of the rim 23 and the bead of the tire 22, and is in contact with the flange of the rim 23 and the bead of the tire 22.

[0109] In this embodiment, some sensor modules 3A are arranged at the outer end 2a (outer rim), and some sensor modules 3A are arranged at the inner end 2b (inner rim). The number of sensor modules 3A arranged at the outer end 2a may be the same as or different from the number of sensor modules 3A arranged at the inner end 2b. All sensor modules 3A may be arranged at only one of the outer end 2a and the inner end 2b.

[0110] The control module 4 processes sensor signals output from multiple sensor modules 3A provided on one rotating body 2. The control module 4 may be provided, for example, at the center of the wheel 21. In the specific example shown in FIG. 25 , the control module 4 includes an AD converter 41, a processor 42, a communication interface 43, a power converter 44, and a power storage device 45. The AD converter 41 and the communication interface 43 may be integrated into the processor 42. The AD converter 41, the processor 42, the communication interface 43, the power converter 44, and the power storage device 45 differ from the AD converter 41, the processor 42, the communication interface 43, the power converter 44, and the power storage device 45 of the sensor module 3, respectively, in that the signals to be processed are multiple sensor signals.

[0111] Next, an example of the arrangement of a plurality of sensor modules 3A will be described with reference to Figs. 26 to 28. Fig. 26 is a diagram showing an example of the arrangement of the sensor modules. Fig. 27 is a diagram showing an example of the sensor signal for each camber angle. Fig. 28 is a diagram showing an example of the sensor signal for each slip angle. In the example shown in Fig. 26, one sensor module 3A is arranged at the outer end 2a (outer rim), and one sensor module 3A is arranged at the inner end 2b (inner rim). The sensor module 3A arranged at the outer end 2a will be referred to as "sensor module 3Ao," and the sensor module 3A arranged at the inner end 2b will be referred to as "sensor module 3Ai."

[0112] Specifically, the sensor module 3Ao is disposed between the wheel 21 (rim 23) and the tire 22 at the outer end 2a. More specifically, the sensor module 3Ao is disposed between the outer flange of the rim 23 and the bead of the tire 22, and is in contact with the outer flange of the rim 23 and the bead of the tire 22. The sensor module 3Ai is disposed between the wheel 21 (rim 23) and the tire 22 at the inner end 2b. More specifically, the sensor module 3Ai is disposed between the inner flange of the rim 23 and the bead of the tire 22, and is in contact with the inner flange of the rim 23 and the bead of the tire 22.

[0113] As the camber angle θ increases, the reaction force that the piezoelectric element 31 of the sensor module 3Ao receives from the road surface increases. As a result, as shown in FIG. 27, as the camber angle θ increases, the peak-to-peak value of the sensor signal (hereinafter sometimes referred to as the "first sensor signal") output from the piezoelectric element 31 of the sensor module 3Ao increases. Furthermore, due to the reaction force received from the road surface, the bead of the tire 22 approaches the outer flange of the rim 23, and the piezoelectric element 31 of the sensor module 3Ao is pressed against the bead of the tire 22 and the outer flange of the rim 23. This reduces the degree of freedom of the piezoelectric element 31 of the sensor module 3Ao. Therefore, as the camber angle θ increases, the vibration after the peak of the first sensor signal is suppressed.

[0114] As the camber angle θ decreases, the reaction force that the piezoelectric element 31 of the sensor module 3Ao receives from the road surface decreases. Therefore, as the camber angle θ decreases, the peak-to-peak value of the first sensor signal decreases. Furthermore, the force that the bead of the tire 22 and the outer flange of the rim 23 apply to the piezoelectric element 31 of the sensor module 3Ao weakens, increasing the degree of freedom of the piezoelectric element 31 of the sensor module 3Ao. Therefore, as the camber angle θ decreases, the vibration after the peak of the first sensor signal increases.

[0115] On the other hand, as the camber angle θ increases, the reaction force that the piezoelectric element 31 of the sensor module 3Ai receives from the road surface decreases. Therefore, as the camber angle θ increases, the peak-to-peak value of the sensor signal (hereinafter sometimes referred to as the "second sensor signal") output from the piezoelectric element 31 of the sensor module 3Ai decreases. Furthermore, the force that the bead of the tire 22 and the inner flange of the rim 23 apply to the piezoelectric element 31 of the sensor module 3Ai weakens, increasing the degree of freedom of the piezoelectric element 31 of the sensor module 3Ai. Therefore, as the camber angle θ increases, the vibration after the peak of the second sensor signal increases.

[0116] As the camber angle θ decreases, the reaction force that the piezoelectric element 31 of the sensor module 3Ai receives from the road surface increases. Therefore, as the camber angle θ decreases, the peak-to-peak value of the second sensor signal increases. Furthermore, due to the reaction force from the road surface, the bead of the tire 22 approaches the inner flange of the rim 23, and the piezoelectric element 31 of the sensor module 3Ai is pressed against the bead of the tire 22 and the inner flange of the rim 23. Therefore, the degree of freedom of the piezoelectric element 31 of the sensor module 3Ai decreases. Therefore, as the camber angle θ decreases, the vibration after the peak of the second sensor signal is suppressed.

[0117] As the slip angle φ increases, the bead of the tire 22 approaches the outer flange of the rim 23, and the piezoelectric element 31 of the sensor module 3Ao is pressed against the bead of the tire 22. Therefore, the degree of freedom of the piezoelectric element 31 of the sensor module 3Ao decreases. Therefore, as shown in FIG. 28, as the slip angle φ increases, the vibration after the peak of the first sensor signal is suppressed. As the slip angle φ decreases, the force with which the bead of the tire 22 and the outer flange of the rim 23 press down on the piezoelectric element 31 of the sensor module 3Ao weakens, and the degree of freedom of the piezoelectric element 31 of the sensor module 3Ao increases. Therefore, as shown in FIG. 28, as the slip angle φ decreases, the vibration after the peak of the first sensor signal increases.

[0118] On the other hand, as the slip angle φ increases, the force with which the bead of the tire 22 and the inner flange of the rim 23 press down on the piezoelectric element 31 of the sensor module 3Ai weakens, increasing the degree of freedom of the piezoelectric element 31 of the sensor module 3Ai. Therefore, as shown in FIG. 28, as the slip angle φ increases, the vibration after the peak of the second sensor signal increases. As the slip angle φ decreases, the bead of the tire 22 approaches the inner flange of the rim 23, so the piezoelectric element 31 of the sensor module 3Ai is pressed down by the bead of the tire 22. Therefore, the degree of freedom of the piezoelectric element 31 of the sensor module 3Ai decreases. Therefore, as shown in FIG. 28, as the slip angle φ decreases, the vibration after the peak of the second sensor signal is suppressed.

[0119] 28, upon receiving the first sensor signal and the second sensor signal, the AD converter 41 may convert each of the signals into a digital signal and output the first sensor signal and the second sensor signal as digital signals to the processor 42. Upon receiving the first digital sensor signal from the AD converter 41, the processor 42 may generate a first section signal by dividing the first sensor signal at a specific section. Upon receiving the second digital sensor signal from the AD converter 41, the processor 42 may generate a second section signal by dividing the second sensor signal at a specific section.

[0120] The process of generating the first interval signal and the second interval signal may be similar to the process of generating the interval signal in the estimation system 1, for example. The processor 42 may estimate the state of the rotating body 2 based on the first interval signal and the second interval signal. The process of estimating the state of the rotating body 2 may be similar to the process of estimating the state of the rotating body 2 in the estimation system 1. The processor 42 may output the estimation result.

[0121] In the estimation system 1A, the same effects as those of the estimation system 1 can be achieved with respect to the configuration common to the estimation system 1. In the estimation system 1A, the piezoelectric element 31 of the sensor module 3Ao and the piezoelectric element 31 of the sensor module 3Ai are arranged on opposite sides of the center of the rotating body 2 in the direction along which the rotation axis AX extends. The piezoelectric element 31 of the sensor module 3Ao may be arranged, for example, on the outer end side of the center of the rotating body 2 in the direction along which the rotation axis AX extends. The piezoelectric element 31 of the sensor module 3Ai may be arranged, for example, on the inner end side of the center of the rotating body 2 in the direction along which the rotation axis AX extends.

[0122] The sensor signal output from the piezoelectric element 31 of the sensor module 3Ao and the sensor signal output from the piezoelectric element 31 of the sensor module 3Ai change differently in response to changes in the state of the rotating body 2. Specifically, as shown in FIGS. 27 and 28, the sensor signal output from the piezoelectric element 31 of the sensor module 3Ao and the sensor signal output from the piezoelectric element 31 of the sensor module 3Ai may change in a contradictory manner. When the state of the rotating body 2 is estimated using two sensor signals that change in a contradictory manner in this way, the influence of disturbances and the like can be reduced. As a result, the accuracy of estimating the state of the rotating body 2 may be improved compared to a configuration (estimation system 1) that estimates the state of the rotating body 2 using a single sensor signal.

[0123] Next, an estimation system according to yet another embodiment will be described with reference to Fig. 29. Fig. 29 is a schematic configuration diagram of an estimation system according to yet another embodiment. Estimation system 1B shown in Fig. 29 differs from estimation system 1 mainly in that it includes a sensor module 3B instead of sensor module 3 and further includes an external device 5B.

[0124] The sensor module 3B differs from the sensor module 3 mainly in that it does not include a processor 42. In the sensor module 3B, the AD converter 41 outputs the sensor signal as a digital signal to the communication interface 43. The communication interface 43 transmits the sensor signal as a digital signal to the external device 5B via the communication network NW1.

[0125] The external device 5B differs from the external device 5 mainly in that it includes a processor 51B instead of the processor 51. The processor 51B differs from the processor 51 mainly in that the processor 51B estimates the state of the rotating body 2 based on a sensor signal transmitted from the sensor module 3B. The processor 51B may be configured to estimate the state of the rotating body 2, for example, in the same manner as the processor 42. The processor 51B may output the estimation result to the output device 54, for example.

[0126] In the estimation system 1B, the same effects as those of the estimation system 1 can be achieved with respect to the configuration common to the estimation system 1. Furthermore, in the estimation system 1B, a processor 51B of the external device 5B estimates the state of the rotating body 2. In this case, for example, restrictions on power consumption, physical size, cooling, and the like are relaxed, so that a processor having a higher computing power than the processor 42 included in the sensor module 3 can be employed as the processor 51B. When such a processor 51B is employed, it is therefore possible to shorten the time required to estimate the state of the rotating body 2.

[0127] Next, an estimation system according to yet another embodiment will be described with reference to Fig. 30. Fig. 30 is a schematic diagram of an estimation system according to yet another embodiment. Estimation system 1C shown in Fig. 30 differs from estimation system 1B mainly in that it includes an external device 5C instead of external device 5B and further includes a server 6.

[0128] The external device 5C differs from the external device 5B mainly in that it includes a processor 51 instead of the processor 51B. The processor 51 is a circuit element that performs control and calculations in the external device 5C, similar to the processor 51 of the external device 5. Upon receiving a sensor signal from the sensor module 3B, the communication interface 55 outputs the sensor signal to the communication interface 56. The communication interface 56 may be configured to transmit the sensor signal to the server 6 via the communication network NW2.

[0129] The server 6 may have, for example, the same hardware configuration as the external device 5C. The processor of the server 6 may estimate the state of the rotating body 2 based on a sensor signal transmitted from the external device 5C. In this case, the processor of the server 6 may estimate the state of the rotating body 2 by, for example, processing similar to that of the processor 42.

[0130] In the estimation system 1C, the configuration common to the estimation system 1B also achieves the same effects as the estimation system 1B. Furthermore, in the estimation system 1C, a processor of the server 6 estimates the state of the rotating body 2. With this configuration, for example, even if a sensor module 3B is installed on the rotating body 2 of a plurality of different vehicles V, there is no need to implement a function for estimating the state of the rotating body 2 in the external device 5 in each vehicle V. In other words, the server 6 can estimate the state of the rotating body 2 provided in each vehicle V based on signals collected via the external device 5 provided in each vehicle V.

[0131] The estimation system, estimation method, and estimation program according to the present disclosure are not limited to the above embodiments.

[0132] For example, the sensor modules 3, 3B and the control module 4 may not include the power converter 44 and the power storage device 45. In this case, the sensor modules 3, 3B and the control module 4 may include a battery or may receive an external power supply.

[0133] In the above embodiment, the sensor modules 3, 3A, 3B (the piezoelectric elements 31 thereof) are arranged at the outer end 2a or the inner end 2b, but they may be arranged at positions according to the configuration of the wheel 21 and the tire 22. The sensor modules 3, 3A, 3B (the piezoelectric elements 31 thereof) may be arranged at a position closer to the outer end or inner end than the center of the rotating body 2 in the direction in which the rotation axis AX extends. In the example shown in FIG. 26, the piezoelectric element 31 of the sensor module 3Ao may be arranged at a position closer to the outer end than the center, and the piezoelectric element 31 of the sensor module 3Ai may be arranged at a position closer to the inner end than the center.

[0134] Any reference to an element using designations such as "first" and "second" used in this disclosure does not limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements. Thus, reference to a first and a second element does not imply that only two elements may be employed, nor that the first element must in some way precede the second element. In this disclosure, the use of a first element does not imply that there is a presumption of the presence of more than one element. [Explanation of symbols]

[0135] 1, 1A, 1B, 1C...estimation system, 2...rotating body, 2a...outer end (first end), 2b...inner end (second end), 3, 3A, 3B...sensor module, 4...control module, 5, 5B, 5C...external device, 21...wheel, 22...tire, 23...rim, 31...piezoelectric element (first sensor, second sensor, sensor), 42...processor, 51, 51B...processor, AX...rotating axis, M...estimation model (machine learning model).

Claims

1. a first sensor that can be disposed between a wheel and a tire mounted on the wheel, the first sensor outputting a first sensor signal corresponding to a pressing force between the wheel and the tire; a processor that generates a first section signal by dividing the first sensor signal into specific sections, calculates a peak-to-peak value from the first section signal, calculates an attenuation rate of the first section signal from the first section signal, and estimates a state of a rotating body including the wheel and the tire based on the attenuation rate and the peak-to-peak value; Equipped with The attenuation rate is a value obtained by dividing a positively convex peak value occurring next to a maximum value in the first section signal by the peak-to-peak value.

2. The estimation system according to claim 1 , wherein the first sensor is disposed between a rim included in the wheel and the tire.

3. the rotating body includes a first end and a second end that are opposite ends of the rotating body in a rotation axis direction, The estimation system according to claim 1 or 2, wherein the first sensor is disposed at a position closer to the first end than to a center of the rotating body in the rotation axis direction.

4. a second sensor that can be disposed between the wheel and the tire and outputs a second sensor signal corresponding to a pressing force between the wheel and the tire; the second sensor is disposed at a position closer to the second end than to the center, The estimation system according to claim 3 , wherein the processor generates a second interval signal by dividing the second sensor signal by the specific interval, and estimates the state further based on the second interval signal.

5. The estimation system according to any one of claims 1 to 4, wherein the specific section is a section corresponding to one rotation of the rotating body.

6. The estimation system according to any one of claims 1 to 5, wherein the processor estimates the state based on a plurality of waveform characteristics that are different from one another and calculated from the first section signal.

7. 7. The estimation system according to claim 6, wherein the plurality of waveform characteristics include a value based on at least one of a maximum value of the first section signal, a minimum value of the first section signal, a difference between the maximum value and the minimum value, a standard deviation of the first section signal, a variance of the first section signal, an average value of the first section signal, a median value of the first section signal, and a value at an inflection point of the first section signal.

8. The estimation system according to any one of claims 1 to 7, wherein the processor estimates the state using a machine learning model for estimating the state.

9. The estimation system according to any one of claims 1 to 8, wherein the state includes at least one of a camber angle, a slip angle, a load applied to the rotating body, and an air pressure.

10. the first sensor and the processor constitute a sensor module; the sensor module is provided on the rotating body, The estimation system according to any one of claims 1 to 9, wherein the processor outputs the estimation result to an external device provided outside the rotating body.

11. the first sensor is a piezoelectric element that generates electrical energy in response to the pressing force, The estimation system according to any one of claims 1 to 10, wherein the processor operates using the electrical energy generated by the piezoelectric element.

12. the first sensor is a piezoelectric element that generates electrical energy in response to the pressing force, The estimation system according to any one of claims 1 to 11, wherein the processor estimates the state of the rotating body by using the voltage or current of the electrical energy generated by the piezoelectric element as the first sensor signal.

13. The estimation system according to any one of claims 1 to 12, wherein the processor estimates the state of the rotating body by comparing the damping rate and the peak-to-peak value with the damping rate and the peak-to-peak value in a reference state of the rotating body, respectively.

14. acquiring a sensor signal corresponding to a pressing force between the wheel and the tire from a sensor disposed between the wheel and the tire; generating a section signal by dividing the sensor signal into specific sections; calculating a peak-to-peak value from the section signal; calculating an attenuation rate of the section signal from the section signal; estimating a state of a rotating body including the wheel and the tire based on the attenuation rate and the peak-to-peak value; Including, An estimation method, wherein the attenuation rate is a value obtained by dividing a positive convex peak value occurring next to the maximum value in the section signal by the peak-to-peak value.

15. acquiring a sensor signal corresponding to a pressing force between the wheel and the tire from a sensor disposed between the wheel and the tire; generating a section signal by dividing the sensor signal into specific sections; calculating a peak-to-peak value from the section signal; calculating an attenuation rate of the section signal from the section signal; estimating a state of a rotating body including the wheel and the tire based on the attenuation rate and the peak-to-peak value; An estimation program that causes a computer to execute the following: An estimation program, wherein the attenuation rate is a value obtained by dividing a positive convex peak value occurring next to the maximum value in the section signal by the peak-to-peak value.

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