Piezoelectric tires

Abstract

Provided is a piezoelectric tire in which peeling and cracking of electrodes constituting a piezoelectric element are suppressed, and durability as a piezoelectric tire is improved. A piezoelectric tire (1A) has a tire main body (2), a coated piezoelectric portion (3), and a circuit unit (4). The coated piezoelectric portion (3) is coated on the tire main body (2) to generate electric power corresponding to a strain generated on a ground contact surface of the tire main body (2). The circuit unit (4) is provided on the tire main body (2) and is driven using the electric power generated by the coated piezoelectric portion (3). By using a coated piezoelectric portion as the piezoelectric portion (3), the piezoelectric portion (3) is in close contact with the tire main body (2), and peeling and cracking of electrodes constituting the piezoelectric portion (3) are suppressed. As a result, the piezoelectric tire (1A) is not impaired in followability to a strain of the tire main body (2), and durability as a piezoelectric tire is improved.

Description

Technical Field

[0001] The present invention relates to a piezoelectric tire that generates electric power according to the strain of a tire contact patch. Background Art

[0002] For example, Patent Document 1 discloses a tire having a power generation device. The power generation device includes a plurality of power generation elements and a capacitor. Each power generation element has two elastic electrodes and an elastic polymer compound (dielectric elastomer) sandwiched therebetween. The elastic polymer compound generates a potential difference between the electrodes based on the strain generated in the tire. The capacitor stores the electrical energy generated by the power generation element. The plurality of power generation elements are arranged on at least one side surface inside the tire on a circumference centered on the rotation axis. The circumferential length of each power generation element is set so as not to simultaneously apply strain caused by compression and strain caused by tension due to the rotating tire contacting the ground.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-223054

[0004] In Patent Document 1, the two electrodes that make up the piezoelectric element (generating element) are formed by bonding, sputtering, or vapor deposition onto the two surfaces of a dielectric elastomer. However, the durability of electrodes formed using such methods is problematic. This is because the strain of the relatively large tires, which are repeated at high frequencies during vehicle operation, can easily cause the electrodes to peel off or break due to the inherently harsh operating conditions of such tires. Summary of the Invention

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress separation and cracking of electrodes constituting a piezoelectric element and to improve the durability of a piezoelectric tire.

[0006] To address this issue, the present invention provides a piezoelectric tire comprising a tire body, a coating-type piezoelectric portion, and a circuit unit. The coating-type piezoelectric portion is applied to the tire body and generates electricity corresponding to the strain generated in the tire body's contact patch. The circuit unit is provided in the tire body and is driven by the electricity generated by the coating-type piezoelectric portion.

[0007] Here, in the present invention, it is preferred that the above-mentioned coated piezoelectric portion is coated on the back side of the ground contact portion of the tire body. In addition, a resin layer may be provided between the coated piezoelectric portion and the tire body so that the coated piezoelectric portion does not directly contact the tire body. In addition, it is preferred that the width direction length of the above-mentioned coated piezoelectric portion is greater than 70% and less than 150% of the ground contact width at the maximum load according to the Japan Automobile Tire Association standard. In addition, it is preferred that the circumferential length of the above-mentioned coated piezoelectric portion is greater than 40% and less than 90% of the ground contact length at the maximum load according to the Japan Automobile Tire Association standard.

[0008] In the present invention, multiple coatable piezoelectric portions may be provided at different locations in at least one of the circumferential and width directions of the tire body. In this case, the multiple coatable piezoelectric portions may have different circumferential lengths and different width lengths. Furthermore, the multiple coatable piezoelectric portions may have a shape obtained by stretching a predetermined shape along at least one of the circumferential and width directions of the tire body.

[0009] In the present invention, the circuit unit may include a wireless circuit that wirelessly transmits signals from a sensor detecting the state of a detection object to the outside. Furthermore, the circuit unit may include a power storage unit that stores power generated by the piezoelectric unit and supplies the stored power to the circuit unit.

[0010] According to the present invention, by configuring the piezoelectric portion disposed on the tire body as a coating type, the piezoelectric portion adheres closely to the tire body and flexibly follows the strain of the tire body. This prevents the electrodes constituting the coating type piezoelectric portion from peeling off or cracking, thereby improving the durability of the piezoelectric tire. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of a piezoelectric tire according to the first embodiment.

[0012] Figure 2 is a cross-sectional view of a piezoelectric tire.

[0013] Figure 3 This is an explanatory diagram of the electromotive force in the piezoelectric portion.

[0014] Figure 4 This is a characteristic diagram of the FEM analysis in the width direction of the tire.

[0015] Figure 5 Graph showing output voltage data when the tire rotates.

[0016] Figure 6 It is a structural diagram of the circuit unit.

[0017] Figure 7 This is a schematic diagram of a piezoelectric tire according to a second embodiment.

[0018] Figure 8 This is a diagram showing the arrangement of multiple piezoelectric units.

[0019] Figure 9 This is a diagram showing the arrangement of a plurality of piezoelectric portions according to the first modification.

[0020] Figure 10 This is a diagram showing the arrangement of a plurality of piezoelectric portions according to the second modification.

[0021] Description of labels

[0022] 1A, 1B: Piezoelectric tire; 2: Tire body; 3, 3a to 3c: Piezoelectric part; 4: Circuit unit; 5: Resin layer; 6: Processing circuit; 7: Wireless circuit; 8: Power storage unit; 9a: Pressure sensor; 9b: Acceleration sensor; 9c: Temperature sensor. DETAILED DESCRIPTION

[0023] (First embodiment)

[0024] Figure 1 This is a schematic diagram of a piezoelectric tire according to a first embodiment. This piezoelectric tire 1A is mounted on an automobile, but while its shape and size vary, it can be widely used on various vehicles, including motorcycles and bicycles. Like conventional tires, piezoelectric tire 1A consists primarily of a tire body 2 formed from an elastic material such as rubber, to which a piezoelectric portion 3 and a circuit unit 4 are attached.

[0025] The piezoelectric portion 3 is provided on the back side of the ground contact portion of the tire body 2 and generates electricity corresponding to the strain generated in the ground contact surface of the tire body 2. The piezoelectric portion 3 includes a pair of electrodes arranged one above the other and a piezoelectric film interposed between the pair of electrodes. In this embodiment, the piezoelectric portion 3 is a piezoelectric portion applied to the inner surface of the tire body 2, i.e., a coating type piezoelectric portion. Examples of coating methods include silk screen printing, screen printing, inkjet printing, coating with a bar coater, and spraying (for example, see Japanese Patent Application Laid-Open No. 2018-157950), but excludes bonding, sputtering, and vapor deposition.

[0026] Specifically, a lower electrode is applied to the inner surface of the tire body 2, and a piezoelectric film is formed on top of the lower electrode. The piezoelectric film is preferably made of a flexible resin-based piezoelectric material such as polyvinylidene chloride (PVDC), polylactic acid (PLA), polyvinylidene fluoride (PVDF), or a copolymer of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) (P(VDF-TrFE)). Furthermore, the upper electrode is formed on top of the piezoelectric film using the same method as the lower electrode.

[0027] By using a coating-type piezoelectric portion as the piezoelectric portion 3, adhesion to the tire body 2 is improved compared to non-coating piezoelectric portions such as those formed by bonding, sputtering, or vapor deposition. This ensures that the piezoelectric portion 3 can follow the strain of the tire body 2 and prevents the electrodes constituting the piezoelectric portion 3 from peeling off or breaking.

[0028] And, as Figure 2As shown, a resin layer 5 may be interposed between the piezoelectric portion 3 and the tire body 2. Generally, the following phenomenon is known: the tire body 2 contains a sulfur component, and as a result of changes over time, the sulfur component floats (seeps) to the surface of the tire body 2. When the piezoelectric portion 3 is in direct contact with the back of the tire body 2, the piezoelectric portion 3 is corroded by the sulfur component that has floated to the surface of the tire body 2, which may cause degradation or deterioration. To solve this problem, a resin layer 5 is interposed between the piezoelectric portion 3 and the tire body 2 as a protective layer to prevent the piezoelectric portion 3 from directly contacting the tire body 2. The resin layer 5 is preferably formed by coating in a manner that does not easily peel off from the tire body 2, and preferably does not contain a sulfur component.

[0029] Figure 3 This is an illustration of the electromotive force in the piezoelectric section 3. Generally, regardless of whether the piezoelectric section 3 is a coated type, as a characteristic of the single detection surface constituting the piezoelectric section 3, when the direction of strain differs locally, for example, when there is a mixture of compressive regions A, where strain is applied, and tensile regions B, where strain is relaxed, an electromotive force of one polarity (e.g., negative) is generated in the compressive region A, while an electromotive force of another polarity (e.g., positive) is generated in the tensile region B. As a result, the electromotive forces of the two polarities cancel each other out, resulting in a decrease in the overall electromotive force of the piezoelectric section 3. The overall electromotive force is maximized when the detection surface is occupied by only regions of one polarity. Furthermore, the overall electromotive force is minimized when half of each region A and half of each region B are mixed. In this case, the positive and negative electromotive forces are completely canceled out, resulting in an overall electromotive force of zero. Therefore, by setting the coating dimensions to avoid the presence of mixed compression and tension (in other words, to cancel out the positive and negative electromotive forces), so that the strain applied to the piezoelectric section 3 is either exclusively compressive or exclusively tensile, the overall electromotive force can be maximized (ensuring power generation). This is true regardless of the circumferential and width directions of the tire.

[0030] Specifically, the inventors conducted experiments and simulations to determine the widthwise length of the piezoelectric portion 3. The results indicate that a value within the range of 70% to 150% of the ground contact width at maximum load, as specified by the Japan Automobile Tire Association (JATMA) standards, is preferred. The tire's rim, load, and internal pressure are referenced from the JATMA standards, and these values ​​are uniquely determined for each tire type.

[0031] Figure 4is a graph in which the width direction strain of the inner surface of the tire is analyzed by FEM (Finite Element Method). In this graph, the horizontal axis indicates the distance from the ground center in % when the ground contact width is set to 100%. Here, the "ground contact width" refers to the maximum straight-line distance in the tire axial direction on the contact surface that contacts the flat plate when the tire is installed on the applicable rim and set to a prescribed air pressure, vertically placed with respect to the flat plate in a stationary state, and a load corresponding to a prescribed mass is applied. The air pressure and load capacity are prescribed in this standard. The vertical axis is the width direction strain (%) and positive is stretching and negative is compression. The load applied to the tire is analyzed at 25%, 58%, and 100% of the JATMA maximum load. As is clear from this graph, the width direction strain distribution is left-right symmetrical (symmetrical on the front side and back side of the tire) with the ground center as the reference.

[0032] In the FEM analysis, the strain is negative from the ground center to the positions of ±36% (72% overall) of the ground contact width even under the load 3 condition. As long as 70% or more of 72% is considered to include deviations and the like caused by disturbance factors and dimensions, the strain is negative regardless of the load size. Also, when the positions of ±72% (144% overall) of the ground contact width are observed from the ground center, the strain is approximately a negative region under the load 25% and 58% conditions, but under the load 100% condition, there are regions in which the strain is positive, and the overall shape is mixed with positive and negative. As long as 150% or less of 144% is considered to include deviations and the like caused by disturbance factors and dimensions, only a negative region is present under the load small condition (when the rear tire is fixed, during braking, and the like).

[0033] On the other hand, regarding the length in the circumferential direction of the piezoelectric portion 3, the inventors have researched through experiments or simulations, and as a result, it is preferable to be 40% or more and 90% or less of the ground contact length when the maximum load of JATMA is loaded.

[0034] Figure 5 is a graph showing the output voltage data when a load is applied to a tire on which the piezoelectric portion 3 is coated and the tire is rotated. The horizontal axis is time and the vertical axis is output voltage. Here, the "ground contact length" refers to the maximum straight-line distance in the tire circumferential direction on the contact surface that contacts the flat plate when the tire is installed on the applicable rim and set to a prescribed air pressure, vertically placed with respect to the flat plate in a stationary state, and a load corresponding to a prescribed mass is applied. The piezoelectric portion coated in this example is the same in the width direction length at three levels of 54%, 81%, and 108% of the circumferential length when the circumferential length is set to 100% of the ground contact length. As is clear from the time-series waveform of the voltage, the voltage is generated earlier than the piezoelectric portion grounds and also after the piezoelectric portion grounds. Also, even if the circumferential length is different, it becomes a generally similar waveform.

[0035] When comparing the voltage levels in this figure, the ground length 81% is the largest, 54% is the second largest, and 108% is the smallest. For the piezoelectric part of 108%, although the amount of piezoelectric elements is the largest among the three levels, the voltage level is small. This is because Figure 3 As shown in the figure, there are regions with compression and tension strain mixed in a piezoelectric element, and the electromotive force is offset by positive and negative, which reduces the overall electromotive force. Therefore, in order to ensure the electromotive force, the circumferential length of the piezoelectric portion to be coated needs to be set to be less than the ground contact length (less than 100% of the ground contact length ratio). On the other hand, the circumferential length of the tire strained by the load is longest at the outermost ground contact portion and is shortest at the inner surface of the tire due to the thickness of the tread component. In the voltage data of this figure, the circumferential length of 81% is the largest. As long as it is less than 100% and less than 90% of the deviation caused by interference factors and size is taken into account on 81%, there will be no mixed regions with positive and negative strain in a piezoelectric element.

[0036] On the other hand, the load during actual driving fluctuates between approximately 25% and 100%. The contact length at 25% of the JATMA's maximum load is approximately 47% of that at 100% load. To prevent positive / negative cancellation within a single piezoelectric section 3 under these conditions, the lower limit is set to 40%. Specifically, the 40% lower limit is sufficient to cover light loads (such as when the vehicle is unladen or when the rear tires are braking) by shortening the contact length to 47% of that at maximum load.

[0037] The circuit unit 4 is provided in the tire body 2 and is driven by the electric power generated by the piezoelectric portion 3 . Figure 6 This is a structural diagram of the circuit unit 4. This circuit unit 4 has the function of wirelessly outputting the output of sensors that detect the state of a detection object to the outside world. It includes a processing circuit 6, a wireless circuit 7, and a power storage unit 8. In this embodiment, the sensors include a pressure sensor 9a, an acceleration sensor 9b, and a temperature sensor 9c. These sensors are located within the tire body 2 or at appropriate locations on the circuit unit 4. The pressure sensor 9a detects the pressure (air pressure) within the tire body 2. The acceleration sensor 9b detects the acceleration of the tire body 2 as it rotates. Furthermore, the temperature sensor 9c detects the temperature within the tire body 2.

[0038] Processing circuit 6 performs signal processing such as A / D conversion and noise removal on the output signals of multiple sensors 9a-9c and outputs the processed signals to wireless circuit 7. Wireless circuit 7 wirelessly transmits the processed signals from sensors 9a-9c to an external device (e.g., a computer inside the vehicle). Furthermore, power storage unit 8 includes a rechargeable battery that stores the power generated by piezoelectric unit 3. This stored power is then supplied to processing circuit 6 and wireless circuit 7 in circuit unit 4.

[0039] Thus, according to the present embodiment, by using the coating type piezoelectric portion as the piezoelectric portion 3 provided to the tire main body 2, the piezoelectric portion 3 is in close contact with the tire main body 2, and thus peeling and breakage of the electrode constituting the piezoelectric portion 3 can be suppressed. As a result, the followability to the strain of the tire main body 2 is not impaired, and improvement in the durability of the piezoelectric tire 1A can be achieved. In this regard, for example, in a case where the piezoelectric element is formed by a method other than coating, such as adhesion of a film, it is difficult to follow the large strain of the tire formed of a soft material, and peeling and breakage of the electrode constituting the piezoelectric element easily occur. Also, in a case where the device type power generating element is mounted, the strain mode and the center of gravity easily deviate. By using the coating type piezoelectric portion 3, these problems can be effectively eliminated.

[0040] Also, according to the present embodiment, by setting the length in the width direction of the piezoelectric portion 3 to be 70% or more and 150% or less of the ground contact width at the time of the maximum load of JATMA and / or setting the length in the circumferential direction of the piezoelectric portion 3 to be 40% or more and 90% or less of the ground contact length at the time of the maximum load of JATMA, the power generation amount can be effectively ensured.

[0041] Further, in the above-described first embodiment, the piezoelectric portion 3 is used for the purpose of supplying electric power to the circuit unit 4, but in addition thereto, it can be used for the purpose of a sensor that detects the ground contact state of the tire main body 2 by a change in the output voltage. In this regard, the same is true for the second embodiment described below.

[0042] (Second Embodiment)

[0043] In the second embodiment, a piezoelectric tire in which a plurality of piezoelectric portions 3 of the first embodiment are arranged is described. Figure 7 is a schematic view of the piezoelectric tire of the second embodiment. Further, the same reference numerals are assigned to the same components as those of the first embodiment, and the description thereof is omitted here.

[0044] The piezoelectric tire 1B has a plurality of piezoelectric portions 3a to 3c provided to the back surface of the ground contact portion of the tire main body 2. These piezoelectric portions 3a to 3c have a prescribed shape, and each generate electric power corresponding to the strain generated on the ground surface of the tire main body 2. By arranging the plurality of piezoelectric portions 3a to 3c at intervals, the entire power generation amount (output voltage) can be increased. Further, in the present embodiment, three piezoelectric portions 3a to 3c are arranged, but the number of arrangements is arbitrary. Also, from the viewpoint of the overall weight balance of the piezoelectric tire 1B and the like, a plurality of piezoelectric portions 3a to 3c can be arranged uniformly in the entire circumferential direction of the tire main body 2.

[0045] Figure 8This diagram illustrates the arrangement of multiple piezoelectric sections 3a-3c. These sections are positioned at different locations along the circumference of the tire body 2. Each piezoelectric section 3a-3c is based on a rectangular shape, but has been stretched along the circumference of the tire body 2. In other words, while the width of the tire body 2 is uniform, the circumferential lengths vary, such as La, Lb, and Lc (La>Lb>Lc).

[0046] The purpose of applying multiple piezoelectric sections 3a to 3c of different circumferential lengths is the same as in the first embodiment described above, which is to ensure the amount of power generated. The ground contact length of the tire is proportional to the load. During actual driving, the load varies between 25% and 100% of the maximum load applied to the JATMA. Furthermore, the compression / stretching of the piezoelectric sections 3a to 3c also depends on the load. That is, when the circumferential length is large and the load is large, only stretching occurs, and the electromotive force increases. Furthermore, when the circumferential length is large and the load is small, compression / stretching coexists, resulting in a loss of electromotive force. On the other hand, when the load is small, the piezoelectric section with a short circumferential length only stretches, and therefore the electromotive force increases compared to the piezoelectric section with a long circumferential length. Therefore, by applying multiple piezoelectric bodies 3a to 3c of different circumferential lengths, the electromotive force can be effectively ensured regardless of the load conditions.

[0047] The shapes of the plurality of piezoelectric parts 3a to 3c are not limited to rectangular shapes, and appropriate shapes may be adopted based on the strain shape of the tire body 2 in the grounded state. Figure 9 As shown in FIG, it can also be a shape that is based on a rhombus and stretched along the circumferential direction of the tire body 2. Figure 10 As shown, a shape obtained by arranging two trapezoids in line symmetry and stretching the shape in the circumferential direction of the tire body 2 may be used as a basis.

[0048] As described above, according to the present embodiment, by providing the plurality of piezoelectric portions 3 a to 3 c having different lengths in the circumferential direction of the tire body 2 , it is possible to effectively ensure the amount of power generated regardless of load conditions.

[0049] Furthermore, in the second embodiment described above, the focus was on the circumferential direction of the tire body 2. However, the multiple piezoelectric portions may alternatively be provided at different positions in the width direction of the tire body 2, or may be provided in both the circumferential and width directions. In this case, the multiple piezoelectric portions provided in the width direction may be formed in a shape that is stretched in the width direction of the tire body 2, similar to the case of the circumferential direction.

[0050] The present invention can be understood not only as an invention of an object such as a piezoelectric tire but also as a method for manufacturing a piezoelectric tire in which the piezoelectric portions 3 and 3 a to 3 c are formed by coating the tire body 2 .

Claims

1. A piezoelectric tire, characterized in that: The piezoelectric tire has: tire body; a coating-type piezoelectric portion that is coated on the tire body and generates electric power corresponding to strain generated on a contact surface of the tire body; and a circuit unit provided in the tire body and driven by the power generated by the coating type piezoelectric portion; The coating type piezoelectric portion is provided in plurality at different positions in at least one of the circumferential direction and the width direction of the tire body. The plurality of coatable piezoelectric portions have different circumferential lengths, and thus an electromotive force can be effectively ensured regardless of load conditions.

2. The piezoelectric tire according to claim 1, wherein The coating-type piezoelectric portion is coated on the back surface of the ground contact portion of the tire body.

3. The piezoelectric tire according to claim 2, wherein: The piezoelectric tire further includes a resin layer interposed between the coating-type piezoelectric portion and the tire body so that the coating-type piezoelectric portion does not directly contact the tire body.

4. The piezoelectric tire according to any one of claims 1 to 3, characterized in that: The length of the coating type piezoelectric portion in the width direction is not less than 70% and not more than 150% of the ground contact width at the time of maximum load according to the Japan Automobile Tire and Tire Association standard.

5. The piezoelectric tire according to any one of claims 1 to 3, characterized in that The circumferential length of the coating-type piezoelectric portion is not less than 40% and not more than 90% of the ground contact length at the time of maximum load according to the Japan Automobile Tire and Tire Association standard.

6. The piezoelectric tire according to any one of claims 1 to 3, characterized in that: The plurality of coatable piezoelectric portions have different lengths in the width direction.

7. The piezoelectric tire according to any one of claims 1 to 3, characterized in that: The plurality of coatable piezoelectric portions have a shape obtained by extending a predetermined shape in the circumferential direction of the tire body.

8. The piezoelectric tire according to any one of claims 1 to 3, characterized in that: The circuit unit includes a wireless circuit that wirelessly transmits a signal from a sensor that detects a state of a detection object to the outside.

9. The piezoelectric tire according to any one of claims 1 to 3, characterized in that: The circuit unit includes a power storage unit that stores the power generated by the piezoelectric unit and supplies the stored power to the circuit unit.

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