Strain detector

Abstract

According to the present invention, a cover of an enclosure for a strain detection device has a cylindrical peripheral wall section, a disc-shaped top plate section that closes the upper end of the peripheral wall section, and a reinforcing section that protrudes from the top plate section. The volume of the cover is at least 15% and less than 40% of the volume of a cylinder including the upper surface of the top plate section, the outer circumferential surface of the peripheral wall section, and the bottom surface of the peripheral wall section. In the strain detection device, the top plate section of the cover has a maximum deformation of at most 4.1% of the outer diameter of the cover, said deformation being in the central axial direction of the peripheral wall section and being due to the differential pressure between the internal pressure of an interior space of a case sealed by the cover and the air pressure of a tire.

Description

[Technical Field]

[0001] The present disclosure relates to a strain sensing device. [Background technology]

[0002] There has been known an invention relating to a functional component that can be attached to a tire (see Patent Document 1 below). This conventional functional component includes a configuration in which a strain detection means (strain sensor) that detects strain in the tire is provided on the bottom surface (Patent Document 1, Claim 6, paragraph 0043, and Figure 10).

[0003] The conventional functional component includes a housing, and the housing includes a housing case having a housing space (housing section) for the module, and a cap that functions as a lid for the housing case (Patent Document 1, paragraphs 0010-0011, Figure 2). A hole penetrating the circular ceiling of the cap is formed, and the hole allows communication between the housing space of the housing case and the outside when the opening of the housing case is closed by the cap (Patent Document 1, paragraph 0016, Figure 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-055402 Summary of the Invention [Problem to be solved by the invention]

[0005] The housing of a strain detector that is attached to the inner surface of the tire opposite the tire contact patch via an elastic adhesive and detects tire strain is composed of, for example, a case that houses a circuit board, a battery, etc., and a cover that closes the opening of the case. Therefore, if a hole is formed in the housing cover, as with the functional part in Patent Document 1, tire air pressure may act on the circuit board or battery inside the housing case, or moisture or dust may enter the inside of the case, which may cause malfunction of the strain detector.

[0006] However, if the holes in the housing cover are closed to create a sealed housing, a uniformly distributed load acts on the cover due to the difference between the internal pressure of the housing and the air pressure in the tire. If the cover deforms due to this uniformly distributed load, stress caused by the deformation of the cover acts on the elastic adhesive between the strain sensor that detects tire strain and the tire, which could cause detection errors in the strain sensor. However, if the thickness of the cover is increased to prevent deformation, the weight of the housing, including the cover, increases, which increases the centrifugal and inertial forces acting on the strain detection device, making tire alignment adjustment more difficult and potentially reducing the performance and practicality of the device.

[0007] The present disclosure provides a strain detection device that can improve the accuracy of tire strain detection by suppressing deformation of the cover of an airtight housing that houses a circuit board and a battery while suppressing an increase in the weight of the housing including the case and cover. [Means for solving the problem]

[0008] One aspect of the present disclosure is a strain detection device comprising: a case fixed to the inner surface of a tire via an elastic adhesive; a strain sensor attached to the outside of the bottom wall of the case and detecting strain in the tire via the elastic adhesive; a circuit board and a battery housed in the internal space of the case; and a resin cover that closes an opening on the opposite side of the bottom wall of the case to seal the internal space, wherein the cover has a cylindrical peripheral wall portion, a circular top plate portion that closes the upper end of the peripheral wall portion, and a reinforcing portion that protrudes from the top plate portion, and the volume of the cover is 15% or more and less than 40% of the volume of a cylinder including the upper surface of the top plate portion, the outer peripheral surface of the peripheral wall portion, and the bottom surface of the peripheral wall portion, and the maximum deformation of the top plate portion of the cover in the central axial direction of the peripheral wall portion due to the pressure difference between the internal pressure of the internal space of the case sealed by the cover and the air pressure of the tire is 4.1% or less of the outer diameter of the cover. [Effects of the Invention]

[0009] According to the above-described aspect of the present disclosure, a tire strain detection device can be provided that can improve the accuracy of tire strain detection by suppressing an increase in the weight of the housing including the case and cover while suppressing deformation of the cover of the sealed housing that houses the circuit board and battery. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an enlarged cross-sectional view showing an embodiment of a strain sensor according to the present disclosure. [Figure 2] 2A and 2B are a bottom view and a cross-sectional view of a cover of a housing in the strain sensor of FIG. 1. [Figure 3] 3A and 3B are a bottom view and a cross-sectional view showing a first modified example of the cover of FIG. 2. [Figure 4] 3A and 3B are a bottom view and a cross-sectional view showing a second modification of the cover of FIG. 2; [Figure 5] 3A and 3B are a bottom view and a cross-sectional view showing a third modified example of the cover of FIG. 2. [Figure 6] 2. FIG. 4 is a bottom view and a cross-sectional view showing a fourth modified example of the cover of FIG. [Figure 7] 10A and 10B are a bottom view and a cross-sectional view showing a fifth modified example of the cover of FIG. 2. [Figure 8] 8 is a graph showing the relationship between the stress acting on the cover of FIGS. 2 to 7 and the volume ratio. [Figure 9] 8 is a graph showing the relationship between the outer diameter and the maximum deformation amount of the covers of FIGS. 2 to 7. [Figure 10] FIG. 2 is a top view showing a modified example of the case of the housing in the strain sensor of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a strain sensor according to the present disclosure will be described with reference to the drawings.

[0012] 1 is an enlarged cross-sectional view showing an embodiment of a strain detector according to the present disclosure. The strain detector 100 of this embodiment is attached to the inner circumferential surface Ti of a tire T of a vehicle such as an automobile, detects strain in the tire T, and transmits the detection result to an external device via wireless communication. The strain detection result transmitted from the strain detector 100 is received by an external device such as an electronic control unit (ECU) via a communication device mounted on the vehicle.

[0013] The strain detector 100 includes, for example, a housing 110, a strain sensor 120, an elastic member 130, a battery 140, and a circuit board 150. The housing 110 includes, for example, a cylindrical case 111 made of resin and having a bottom, and a resin cover 112 that closes an opening 111a of the case 111. From the viewpoint of enabling wireless communication, the resin material of the case 111 and the cover 112 can be, for example, polybutylene terephthalate (PBT), polyamide (PA), polycarbonate (PC), or the like, which has a dielectric constant of less than 4 and a dielectric dissipation factor of less than 0.02.

[0014] The case 111 has, for example, a cylindrical portion 111c having a circular opening 111a at its upper end, and a bottom wall 111b that closes the lower end of the cylindrical portion 111c. The case 111 has, for example, a skirt-shaped elastic member 130 attached to the lower end of the cylindrical portion 111c, and is fixed to the inner circumferential surface Ti of the tire T via an elastic adhesive EA filled inside the elastic member 130.

[0015] Cover 112 is fixed to the upper end of cylindrical portion 111c of case 111, for example, by adhesive, and closes opening 111a on the opposite side of bottom wall 111b of case 111, thereby sealing internal space 111d of case 111. Cover 112 has a cylindrical peripheral wall portion 112a and a disk-shaped top plate portion 112b that closes the upper end of peripheral wall portion 112a.

[0016] The strain sensor 120 is attached to the outside of the bottom wall 111b of the case 111 of the housing 110, and detects the strain of the tire T via an elastic adhesive EA. The strain sensor 120 includes, for example, a semiconductor sensor. The semiconductor sensor utilizes the piezo-resistance effect of a diffused resistor formed by ion-implanting impurities into a silicon single crystal, and can detect the strain of the tire T by measuring the voltage directly from the electrode pads of the semiconductor chip. The strain sensor 120 is connected to the circuit board 150 via, for example, wiring 121.

[0017] The lower part of the case 111 is inserted inside the cylindrical upper part of the elastic member 130, and the elastic member 130 is fixed to the outer peripheral surface of the lower part of the case 111. The elastic member 130 has a skirt-shaped lower part whose diameter increases as it moves downward from the cylindrical upper part. The elastic member 130 is made of an elastic resin material such as rubber, and elastically deforms in response to deformation of the tire T.

[0018] Battery 140 is, for example, a button-type battery, and is housed in internal space 111d of case 111 of housing 110 through opening 111a of case 111, and is disposed on bottom wall 111b of case 111. Battery 140 is connected to circuit board 150 via connection terminals 141 and 142, for example, and supplies power to circuit board 150.

[0019] The circuit board 150 is housed, for example, through the opening 111a of the case 111 into the internal space 111d of the case 111, and is supported by steps and protrusions on the inner circumferential surface of the case 111, and is disposed on the battery 140. The circuit board 150 includes, for example, a power supply circuit, a signal processing circuit, a wireless communication circuit, and a control circuit. The power supply circuit, for example, supplies power supplied from the battery 140 to the strain sensor 120. The signal processing circuit, for example, processes a signal input from the strain sensor 120. The wireless communication circuit, for example, transmits the detection result of the strain of the tire T by the strain sensor 120 to an external device via wireless communication. The control circuit, for example, controls the power supply circuit, the signal processing circuit, and the wireless communication circuit.

[0020] The upper and lower figures in Fig. 2 are a bottom view and a cross-sectional view, respectively, of the cover 112 of the housing 110 in the strain detector 100 of Fig. 1. The strain detector 100 of this embodiment is characterized by the following configuration: The cover 112 has a cylindrical peripheral wall portion 112a, a disk-shaped top plate portion 112b that closes the upper end of the peripheral wall portion 112a, and a reinforcing portion 112c that protrudes from the top plate portion 112b.

[0021] The volume of cover 112 is 15% or more and less than 40% of the volume of a cylinder or column including the upper surface of top plate portion 112b, the outer peripheral surface of peripheral wall portion 112a, and the lower surface of peripheral wall portion 112a. Cover 112 is also configured so that the maximum deformation amount of top plate portion 112b of cover 112 in the central axial direction of peripheral wall portion 112a due to the pressure difference between the internal pressure of internal space 111d of case 111 sealed by cover 112 and the air pressure of tire T is 4.1% or less of the outer diameter of cover 112.

[0022] Here, the air pressure of tire T is, for example, a maximum of about 14 [atm] in a commercial tire, whereas the internal pressure of internal space 111d of case 111 sealed by cover 112 is, for example, about 1 [atm]. Due to the pressure difference between the air pressure of tire T and the internal pressure of internal space 111d of case 111, a uniformly distributed load acts on the upper surface of top plate portion 112b of cover 112.

[0023] As described above, the strain detector 100 of this embodiment is provided with the reinforcing portion 112c on the cover 112, and specifies the percentage of the volume of the cover 112 relative to the volume of a cylinder or column defined by the top surface, outer circumferential surface, and bottom surface of the cover 112, which has the peripheral wall portion 112a and the top plate portion 112b. Furthermore, the strain detector 100 of this embodiment specifies the percentage of the maximum deformation of the cover 112 due to the uniformly distributed load relative to the outer diameter of the cover 112.

[0024] An example of the configuration of cover 112 that satisfies these conditions is shown in Figure 2. In the example shown in Figure 2, reinforcing portion 112c includes multiple ribs 112d extending radially from the center of the underside of top plate portion 112b toward the outer edge. Cover 112, for example, satisfies the above-mentioned conditions for volume and maximum deformation of cover 112 and includes three or more ribs 112d arranged at equal angular intervals around the periphery of cover 112. In the example shown in Figure 2, the protruding height of each rib 112d, i.e., the height from the bottom surface of top plate portion 112b to the tip of rib 112d in the protruding direction of rib 112d, is uniform.

[0025] The upper and lower figures in Fig. 3 are a bottom view and a cross-sectional view, respectively, showing Variation 1 of cover 112 in Fig. 2. In cover 112 shown in Fig. 3, for example, the above-mentioned volume and maximum deformation conditions are satisfied, and reinforcing portion 112c includes multiple ribs 112d and cylindrical protrusion 112e. Cylindrical protrusion 112e is a thick-walled portion with a short axis and a cylindrical shape that is concentric with peripheral wall portion 112a and is provided on the underside of top plate portion 112b.

[0026] 3, for example, the width w of the rib 112d, the thickness t of the top plate portion 112b, and the protruding height h of the rib 112d are equal (w=t=h). Also, the radius r2 of the cylindrical protrusion 112e is, for example, equal to or greater than half the radius r1 of the cover 112 (r2≧1 / 2×r1). These conditions are optimal conditions for suppressing deformation of the cover 112, determined, for example, by computer-aided engineering (CAE).

[0027] The upper and lower figures in Fig. 4 are a bottom view and a cross-sectional view, respectively, showing Modification 2 of cover 112 in Fig. 2. Cover 112 shown in Fig. 4 satisfies the above-mentioned volume and maximum deformation conditions, and includes reinforcing portion 112c and multiple ribs 112d arranged at equal angular intervals around the circumferential direction of cover 112. Furthermore, the protruding height h of each rib 112d gradually decreases from the center of top plate portion 112b toward the outer edge.

[0028] The upper and lower figures in Fig. 5 are a bottom view and a cross-sectional view, respectively, showing Modification 3 of cover 112 in Fig. 2. Cover 112 shown in Fig. 5 satisfies the above-mentioned volume and maximum deformation conditions, and further includes reinforcing portion 112c including multiple ribs 112d arranged at equal angular intervals around the circumference of cover 112. Furthermore, the width w of each rib 112d, which is perpendicular to the radial direction of cover 112, gradually decreases from the center of top plate portion 112b toward the outer edge.

[0029] The upper and lower figures in Fig. 6 are a bottom view and a cross-sectional view, respectively, showing Variation 4 of the cover in Fig. 2. Cover 112 shown in Fig. 6 satisfies the above-mentioned volume and maximum deformation conditions, and in place of the multiple ribs 112d, reinforcing portion 112c includes conical protrusion 112f that is concentric with top plate portion 112b and has its bottom surface aligned with the upper surface of top plate portion 112b. Note that cover 112 may also include conical protrusion 112f that is concentric with top plate portion 112b and has its bottom surface aligned with the bottom surface of top plate portion 112b.

[0030] The upper and lower figures in Fig. 7 are a bottom view and a cross-sectional view, respectively, showing Variation 5 of the cover in Fig. 2. Cover 112 shown in Fig. 7 satisfies the above-mentioned volume and maximum deformation conditions, and reinforcing portion 112c includes a tessellated lattice structure 112g instead of multiple ribs 112d. The tessellated shape of lattice structure 112g of cover 112 shown in Fig. 7 may be a regular hexagon, an equilateral triangle, or a square, for example.

[0031] 8 is a graph showing the relationship between the maximum stress σ acting on the top plate portion 112b of the cover 112 shown in Figures 2 to 7 and the volume ratio VR of the cover 112 to a reference cylinder or column. Here, the volume of the reference cylinder or column is the volume of a cylinder or column defined by the top surface of the top plate portion 112b of the cover 112, the outer circumferential surface of the peripheral wall portion 112a, and the bottom surface of the peripheral wall portion 112a.

[0032] 8, the hatched area BA indicates the area where the cover 112 is damaged. The dashed line and filled triangles indicate Comparative Example CE, which is a cover 112 having a peripheral wall portion 112a and a top plate portion 112b, but without a reinforcing portion 112c in which the thickness of the top plate portion 112b is increased. The solid line and open circles indicate the cover 112 according to embodiment E in FIGS. 2 to 7.

[0033] As shown in Fig. 8, in Comparative Example CE in which the thickness of top panel portion 112b is increased, damage to cover 112 can be prevented when volume ratio VR exceeds 40%. In contrast, in Embodiment E in which cover 112 has reinforcing portion 112c, damage to cover 112 can be prevented by setting volume ratio VR to 15% or more. Furthermore, cover 112 according to Embodiment E in Figs. 2 to 7 can be made lighter in weight than cover 112 of Comparative Example CE, which is capable of preventing damage, by setting volume ratio VR to 15% or more and less than 40%.

[0034] 2 to 7. In the graph of Fig. 9, the hatched area BA indicates the area where the cover 112 is damaged. Here, the maximum deformation amount DA of the cover 112 is the maximum deformation amount of the top plate portion 112b of the cover 112 in the central axial direction of the peripheral wall portion 112a due to the pressure difference between the internal pressure of the internal space 111d of the case 111 sealed by the cover 112 and the air pressure of the tire T.

[0035] 9, the solid line and the open circles indicate the cover 112 according to embodiment E in FIGS. 2 to 7. The graph in FIG. 9 indicates that, for example, if the outer diameter Φ of the cover 112 is less than 34 mm, the maximum deformation amount DA of the top plate portion 112b of the cover 112 shown in FIGS. 2 to 7 is less than 1.4 mm, which is 4.1% or less of the outer diameter Φ of the cover 112. This relationship between the outer diameter Φ of the cover 112 and the maximum deformation amount DA can be derived, for example, by CAE.

[0036] Fig. 10 is a top view showing a modified example of the case 111 of the housing 110 in the strain detector 100 of Fig. 1. The case 111 shown in Fig. 10 has a cylindrical portion 111c, a bottom wall 111b that closes the lower end of the case 111, and a plurality of ribs 111e that protrude radially inward from the inner circumferential surface of the cylindrical portion 111c and support a plurality of ribs 112d of the cover 112 shown in Fig. 3.

[0037] 10, the support protrusions 111e have a generally semicircular shape when viewed from the central axis direction of the case 111, and extend from the opening 111a to the bottom wall 111b along the central axis direction of the cylindrical portion 111c of the case 111. The multiple support protrusions 111e are provided at the same angular intervals as the multiple ribs 112d of the cover 112. As a result, the upper surface of each support protrusion 111e of the case 111 contacts the end of the lower surface of each rib 112d of the cover 112, which is adjacent to the peripheral wall portion 112a. Each rib 112d of the cover 112 is supported from below by each support protrusion 111e of the case 111.

[0038] The operation of the strain detector 100 of this embodiment will be described below.

[0039] As described above, the strain detector 100 of this embodiment includes a case 111, a strain sensor 120, a battery 140, a circuit board 150, and a resin cover 112. The case 111 is fixed to the inner circumferential surface Ti of the tire T via an elastic adhesive EA. The strain sensor 120 is attached to the outside of the bottom wall 111b of the case 111 and detects strain of the tire T via the elastic adhesive EA. The battery 140 and the circuit board 150 are housed in an internal space 111d of the case 111. The cover 112 closes the opening 111a on the side opposite the bottom wall 111b of the case 111 to seal the internal space 111d. The cover 112 has a cylindrical peripheral wall 112a, a disc-shaped top plate 112b that closes the upper end of the peripheral wall 112a, and a reinforcing portion 112c that protrudes from the top plate 112b. The volume of this cover 112 is 15% or more and less than 40% of the volume of a cylinder including the upper surface of the top plate portion 112b, the outer peripheral surface of the peripheral wall portion 112a, and the bottom surface of the peripheral wall portion 112a. Furthermore, in the strain detector 100, the maximum deformation amount DA of the top plate portion 112b of the cover 112 in the central axial direction of the peripheral wall portion 112a due to the pressure difference between the internal pressure of the internal space 111d of the case 111 sealed by the cover 112 and the air pressure of the tire T is 4.1% or less of the outer diameter Φ of the cover 112.

[0040] With this configuration, the strain detector 100 of this embodiment can reinforce the cover 112 with the reinforcing portion 112c. More specifically, providing the reinforcing portion 112c to the cover 112 makes it possible to uniformly distribute stress when a uniformly distributed load caused by the pressure difference between the internal space 111d of the case 111 and the air pressure of the tire T acts on the cover 112. This makes it possible to suppress deformation of the cover 112 due to the uniformly distributed load. Furthermore, since the volume of the cover 112 is 15% or more and less than 40% of the volume of a reference cylinder including the upper surface of the top plate portion 112b, the outer circumferential surface of the peripheral wall portion 112a, and the bottom surface of the peripheral wall portion 112a, the weight of the cover 112 can be reduced compared to when the top plate portion 112b of the cover 112 is made thicker. Furthermore, by setting the maximum deformation amount DA due to the pressure difference between the internal pressure of the internal space 111d of the case 111 and the air pressure of the tire T to 4.1% or less of the outer diameter Φ of the cover 112, it is possible to prevent damage to the center of the cover 112. Therefore, according to this embodiment, it is possible to provide a strain detector 100 that can improve the strain detection accuracy of the tire T by suppressing deformation of the cover 112 of the sealed housing 110 that houses the circuit board 150 and the battery 140 while suppressing an increase in the weight of the housing 110 including the case 111 and the cover 112.

[0041] In the strain detector 100 of this embodiment, the reinforcing portion 112c of the cover 112 includes a plurality of ribs 112d extending radially from the center to the outer edge of the lower surface of the top plate portion 112b, as shown in FIGS.

[0042] With this configuration, the strain detector 100 of this embodiment has the multiple ribs 112d, which improve the mechanical strength of the cover 112 against the uniformly distributed load caused by the differential pressure, thereby suppressing deformation of the cover 112. Furthermore, by improving the mechanical strength of the cover 112 with the multiple ribs 112d, it is possible to thin the portion of the top plate portion 112b where the reinforcing portion 112c is not provided, thereby suppressing an increase in the weight of the cover 112. Furthermore, by having three or more ribs 112d on the cover 112, it is possible to make the stress distribution in the cover 112 more uniform and suppress deformation.

[0043] In the strain detector 100 of this embodiment, the reinforcing portion 112c of the cover 112 may include a cylindrical protrusion 112e concentric with the peripheral wall portion 112a provided on the lower surface of the top plate portion 112b, as shown in FIG.

[0044] With this configuration, the strain detector 100 of this embodiment can reinforce the center of the top plate 112b of the cover 112, where the amount of deformation due to the uniformly distributed load caused by the differential pressure is greatest, with the cylindrical protrusion 112e. As a result, the stress distribution when the uniformly distributed load acts on the cover 112 can be made more uniform.

[0045] In the strain detector 100 of this embodiment, the plurality of ribs 112d of the cover 112 have a protruding height h that gradually decreases from the center of the top plate portion 112b toward the outer edge, as shown in FIG.

[0046] With this configuration, in the strain detector 100 of this embodiment, the mechanical strength of the ribs 112d against the uniformly distributed load acting on the top plate portion 112b of the cover 112 is higher at the center than at the periphery of the top plate portion 112b. As a result, the center of the top plate portion 112b, where the amount of deformation is greatest when the uniformly distributed load is applied, can be reinforced by the ribs 112d, which have a higher mechanical strength at the center than at the periphery. This makes the stress distribution in the cover 112 more uniform, and more effectively suppresses deformation of the top plate portion 112b of the cover 112. Furthermore, the protruding height h of the ribs 112d gradually decreases toward the outer edge of the top plate portion 112b, where the amount of deformation when the uniformly distributed load is applied decreases, thereby reducing the weight of the reinforcing portions 112c and suppressing an increase in the weight of the cover 112.

[0047] In the strain detector 100 of this embodiment, as shown in FIG. 5, the width w of the plurality of ribs 112d of the cover 112, which is perpendicular to the radial direction of the cover 112, gradually decreases from the center of the top plate portion 112b toward the outer edge.

[0048] With this configuration, in the strain detector 100 of this embodiment, the mechanical strength of the ribs 112d against the uniformly distributed load acting on the top plate portion 112b of the cover 112 is higher at the center than at the periphery of the top plate portion 112b. As a result, the center of the top plate portion 112b, where the amount of deformation is greatest when the uniformly distributed load is applied, can be reinforced by the ribs 112d, which have a higher mechanical strength at the center than at the periphery. This makes the stress distribution in the cover 112 more uniform, and more effectively suppresses deformation of the top plate portion 112b of the cover 112. Furthermore, by gradually reducing the width w of the ribs 112d toward the outer edge of the top plate portion 112b, where the amount of deformation when the uniformly distributed load is applied decreases, the weight of the reinforcing portion 112c can be reduced, and an increase in the weight of the cover 112 can be suppressed.

[0049] In the strain detector 100 of this embodiment, the reinforcing portion 112c of the cover 112 may include, as shown in FIG. 6, a conical protrusion 112f that is concentric with the peripheral wall portion 112a and whose bottom surface is the upper surface of the top plate portion 112b.

[0050] With this configuration, in the strain detector 100 of this embodiment, the protruding height of the conical protrusions 112f from the upper surface of the top plate portion 112b increases from the outer edge of the top plate portion 112b toward the center. Therefore, the mechanical strength of the conical protrusions 112f against the uniformly distributed load acting on the cover 112 increases from the outer edge toward the center of the top plate portion 112b. By reinforcing the top plate portion 112b of the cover 112 with such conical protrusions 112f, it is possible to make the stress distribution when the uniformly distributed load acts on the cover 112 more uniform, and to more effectively suppress deformation of the cover 112.

[0051] In the strain sensor 100 of this embodiment, the reinforcing portion 112c of the cover 112 can include a tessellated lattice structure 112g as shown in FIG.

[0052] With this configuration, the strain detector 100 of this embodiment can reinforce the top plate portion 112b of the cover 112 with the lattice structure 112g, thereby suppressing deformation of the cover 112. Furthermore, by configuring the reinforcing portion 112c with the lattice structure 112g having many voids, an increase in the volume of the cover 112 can be suppressed, and an increase in the weight of the cover 112 can also be suppressed.

[0053] Furthermore, in the strain detector 100 of this embodiment, the case 111 can have, as shown in FIG. 10, a cylindrical portion 111c, a bottom wall 111b that closes the lower end of the cylindrical portion 111c, and a plurality of support protrusions 111e that protrude radially inward from the inner surface of the cylindrical portion 111c and support a plurality of ribs 112d of the cover 112.

[0054] With this configuration, according to the strain detector 100 of this embodiment, the end of each of the ribs 112d adjacent to the peripheral wall portion 112a of the cover 112 can be supported from below by each of the support protrusions 111e of the case 111. This makes it possible to suppress deformation of each of the ribs 112d when the uniformly distributed load acts on the cover 112, thereby suppressing deformation of the cover 112. Furthermore, since the cylindrical portion 111c of the case 111 has higher mechanical strength against the uniformly distributed load caused by the pressure difference than the disk-shaped top plate portion 112b of the cover 112, it is possible to thin the portions where the cylindrical protrusions 112e are not provided and suppress an increase in the weight of the case 111.

[0055] As described above, according to this embodiment, it is possible to provide a strain detection device 100 that can improve the strain detection accuracy of the tire T by suppressing deformation of the cover 112 of the sealed housing 110 that houses the circuit board 150 and the battery 140 while suppressing an increase in the weight of the housing 110 including the case 111 and the cover 112.

[0056] The above describes an embodiment of the strain detection device according to the present disclosure, but the strain detection device according to the present disclosure is not limited to the above-described embodiment, and additions, omissions, substitutions, and other modifications to the configuration are possible within the scope of the spirit of the present disclosure. [Explanation of symbols]

[0057] 100 Strain detector 111 cases 111a opening 111b Bottom wall 111c Cylindrical part 111d Interior space 111e Support protrusion 112 Cover 112a Peripheral wall section 112b Top plate 112c Reinforcement part 112d Rib 112e Cylindrical convex part 112f Conical convex part 112g lattice structure 120 Strain Sensor 140 batteries 150 Circuit Boards DA Maximum deformation EA Elastic Adhesive T Tire Ti inner surface w width h Projection height Φ Outer diameter

Claims

1. A strain detection device comprising: a case fixed to an inner peripheral surface of a tire via an elastic adhesive; a strain sensor attached to the outside of a bottom wall of the case and detecting strain of the tire via the elastic adhesive; a circuit board and a battery housed in an internal space of the case; and a resin cover that closes an opening on the side of the case opposite the bottom wall to seal the internal space, the cover has a cylindrical peripheral wall portion, a disk-shaped top plate portion that closes an upper end of the peripheral wall portion, and a reinforcing portion that protrudes from the top plate portion, a volume of the cover is 15% or more and less than 40% of a volume of a cylinder including an upper surface of the top plate portion, an outer peripheral surface of the peripheral wall portion, and a bottom surface of the peripheral wall portion; a maximum deformation amount of the top plate portion of the cover in the central axial direction of the peripheral wall portion due to a pressure difference between the internal pressure of the internal space of the case sealed by the cover and the air pressure of the tire, the maximum deformation amount being 4.1% or less of an outer diameter of the cover; Strain detection device.

2. The reinforcing portion includes a plurality of ribs extending radially from a central portion of the lower surface of the top plate portion toward an outer edge portion. The strain sensor according to claim 1 .

3. The reinforcing portion includes a cylindrical protrusion provided on the lower surface of the top plate portion and concentric with the peripheral wall portion. The strain sensor according to claim 2 .

4. The plurality of ribs are characterized in that the protruding height gradually decreases from the center of the top plate portion toward the outer edge. The strain sensor according to claim 2 .

5. The width of the plurality of ribs perpendicular to the radial direction gradually decreases from the center of the top plate portion toward the outer edge thereof. The strain sensor according to claim 2 .

6. The reinforcing portion includes a conical convex portion concentric with the peripheral wall portion and having an upper surface of the top plate portion as a bottom surface. The strain sensor according to claim 1 .

7. The reinforcing portion includes a regular tessellated lattice structure. The strain sensor according to claim 1 .

8. the case has a cylindrical portion, a bottom wall that closes a lower end of the cylindrical portion, and a plurality of support protrusions that protrude radially inward from an inner peripheral surface of the cylindrical portion and support the plurality of ribs of the cover, The strain sensor according to claim 2 .

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